Another option I like is providing some amount of free credit that doesn't expire. So you're not on the hook for providing a "free tier" forever, but users can play around with your service at their own pace.
Like a few weeks ago I was motivated to learn some music production software, so I downloaded a few trial versions. I worked on it heavily for a few days, but then got busy with other things, and now that 30 day trial or whatever is coming up to an end, but I still don't feel like I've had a chance to decide if it works for me, because I haven't been actively using it that long yet still. I do plan to go back to it, just maybe not for another week or two.
But if it only counted the days I opened the application, I'd still have like 26 'days' left to evaluate them (they might, I haven't checked), and it'd be no big deal, and I wouldn't have to feel all stressed out because I'm 'wasting' the demo time by actually having a life and maybe badly timing when to trigger the trial period.
Sometimes there's a shifting business priority, and guess which wins when the choice is "important customer X is on fire" vs "our developer trial for wizbang component xyz is going to expire in 8 days".
Where they don't make sense is for subscriptions, because subscriptions are by definition something your users will be using for a long time, and it might take them a while to realize all of its value and get hooked.
For this stuff a free tier that funnels customers to the paid tiers usually works best. You can play with limitations by restricting features, or usage, or anything else, but you probably shouldn't restrict them based on how much time has elapsed since they first signed up. Let them get hooked at their own pace.