These timelines are wildly optimistic. Boundless is selling a service and I'd recommend nobody actually uses it because you're really paying for nothing. Things like "you are responsible for the information you provide". Part of the reason you get an immigration attorney is to identify likely issues, go with you for your interview, know when (or even if) to apply for an immigration benefit and to put their name as the preparer (ie putting their reputation and career on the line for their advice).
Boundless seems like knowing a guy in the neighbourhood who helps you fill out immigration forms, typically called "notarios". Some will call themselves "paralegals" without working for an actual lawyer. It's a scammy business.
So here's the general process.
1. Petitioner (US citizen or LPR) files an I130 and I130A for their overseas spouse. That requires a lot of documentation to prove your status, that it's a bona fide marriage, biographic information for your spouse, proof that you're both free to marry (ie evidence of previous marriages and that you're divorced/single);
2. USCIS spends 12-15 months processing this. It then gets sent to the National Visa Center ("NVC") who spend another 3+ months looking at the documents, after which you're "documentarily qualified" ("DQ");
3. At this point, your foreign spouse can now make an appointment with an embassy or consulate for an immigrant visa interview. Depending on their country this may be realtively quick (within 1-2 months) or really long (12+ months);
4. The foreign spouse will need to get a medical exam done to check for vaccines, communicable diseases (eg TB), etc. This has to be done within a certain period of the interview;
5. The interview happens and the officer asks whatever they want to ask. If it's approved, your pay the fee and your passport is stamped. You're given a packet to hand over to CBP when you enter the US. It can be denied. The officer may ask for more information, which can add months of delay. Or it can go into a limbo called "admin processing";
6. The spouse travels to the US and is now a permanent resident, assuming CBP lets them in (they have discretion not to btw). You may then have to wait for months for your green card and you're waiting for that to get your SSN so you can work, get a bank account, get on a lease, etc.
It's more realistic to say this will take 2-2.5 years and maybe take 4+. In that entire time the foreign spouse won't get any kind of visa to visit the US so if you want to be with your spouse, you need to live in another country or visit often for a very long time.
So how can go wrong? Lots of ways. Here's a non-exhaustive list:
1. The foreign spouse's entire immigration history is under scrutiny. If they visited their then partner(before getting married) and didn't tell the embassy or CBP about that, it can raise misrep[resentation] issues. and may just cause delays;
2. If they've ever applied for a visa and been denied, this too will be scrutinized;
3. Ideally you only need a police report for the country you live in (to prove no criminal history) and that's relatively easy to get. It might not be. Or you may need it for a bunch of countries if you've lived in multiple over the previous 5 years;
4. USCIS gets to decide where your interview is going to be. Prior to this administration, that could be where you were living. For example, if you were from Mali but living and working in the UK, then you could schedule it in the UK. Now the administration has decided you must be interviewed in your country of birth. If that country has no US embassy (eg Afghanistan) then maybe your country of residence can be used or it might be a country neighbouring your country of birth;
5. What if you applied for asylum from that country? Let's say you are from belarus but claimed (and received) asylum in the UK. You might spend a year trying to tell USCIS that you can't travel to Belarus for your interview;
6. How did the US citizen (or LPR) get their green card? Was it through marriage? This is what USCIS calls a "pivot case" and they view it harshly, particularly if, for example, a Ghana man was married in Ghana, travelled to the US, got divorced in the US, married a US citizen, got citizenship themselves, got divorced and then married somebody else from Ghana. USCIS is increasingly taking the position that this may well be immigration fraud, arguing the man had multiple wives, the divorce was a sham and the second spouse was their spouse all along. It's up to you to prove that's not the case. In this administration that can lead to revocation of their green card or even denaturalization;
7. Was the foreign spouse ever in a cultural or religious marriage? This gets real tricky because what counts as "married" and "divorced" varies by country and, depending on the country, can be hard to prove. Also, some countries have a lot of falsified divorce decrees (eg Nigeria). This can add months as you have to prove they were free to marry;
8. The president may come along and decide to ban visa issuance to your foreign spouse's country. USCIS seemingly takes the broadest definition of this. So if you were born in one of those countries OR have ever had citizen, you're covered by the ban. There's no judicial recourse for this, thanks to Trump v. Hawaii. If so, you're just in limbo probably until Trump leaves office;
9. The black hole after the interview can be "administrative processing". This can mean anything. It can mean something as simple as "we don't like this case". IIRC I heard that 85% of cases in admin processing ultimately get approved but the case may sit in limbo for years and may take a court challenge to resolve it;
10. If you end up taking too long after your interview, your medical exam may expire and you have to do it again. Hopefully the embassy officer asks you for an updated copy but they don't have to be that nice;
11. Between the interview and coming to the US things can happen that USCIS or CBP argue are of material interest. Maybe you get charged with something, even if it's just a traffic offense. You might not fill out the forms correctly. You might not even be aware of it. It might not stop USCIS or CBP making a big deal out of it; and
12. CBP can arbitrarily decide to deny you entry at a port-of-entry even with a valid immigrant visa stamp in your passport for pretty much any reason.
I dare you to find any marriage immigration benefit that's as capricious, arbitrary, time-consuming, restrictive and Byzantine as the US system.