Contractually, any new employer in the same market is going to want to make sure that you're allowed to work for them, that you won't be in breach of any non-competes, non-disclosure, or confidentiality agreements both with your startup and its customers.
Companies large enough to have an HR department, or small enough that hiring is a low priority, won't be able to turn on a dime and make you an offer right away. It can take weeks to get your resume reviewed internally, weeks to schedule interviews, and weeks to make an offer. You need to start applying right away because you're potentially going to be unemployed for three to six months. Better two of those months be while you still have a paycheck.
In interviews, coming from a startup is going to be a red flag for larger companies. If I were interviewing you, I'd grill you pretty hard about whether you really wanted to be an employee, or whether you were just licking your wounds until your next startup was ready to go, and then you'd bail on us. If I had any sense you were a flight risk, or you might be dissatisfied working on a team instead of in a multiple-hats/leadership position, it doesn't matter if you were perfect for the job, you'd get a "no," because companies want people who will stick around.
All of that said, now's a great time to be looking: everyone's back from vacation, and they all have new budgets to start spending (or are getting things lined up to), because fiscal years often start Jan.1 or Apr.1.