Finally got a new job but scared my current employer will withhold bonus

After years of looking for a new job I finally am getting out!! I’ve been looking to escape from family law for 2 years now but haven’t received any offers. I finally got one which seems almost too good to be true - $50K more base pay than I make now, health insurance is completely paid, no billable hours, and an 8-5 schedule (sometimes 8-6, but no weekends). I’m waiting for the other shoe to drop but there are no major red flags so far.

At my current job, I’m on a quarterly bonus system. Our 4th quarter bonus (September - December) is paid out on the second pay period of January, so scheduled for January 24. I already earned that bonus in my mind - it’s purely receivables based. I brought in about $110K last quarter and should receive a $12K bonus or about $7,500 post tax.

I received this job offer yesterday, and they want an answer by Monday. They want me to put in my 2 weeks right away, so also on Monday. I’m scared that my firm will withhold this bonus because they are spiteful and don’t take well to people who quit (I’ve seen many assistants and attorneys come and go while I’ve been here, and the bosses are incredibly hostile). If I give in my notice on Monday, I’ll technically be employed through the date of my bonus check. But I’m also scared that if I give in my notice before that pay day, they will withhold my bonus. Their employee policy says something generally about how all pay is at their discretion, but they never had an officially policy on bonuses - the instructions for how the quarterly bonus works is in an email which doesn’t say anything about if the bonus is guaranteed or discretionary.

I was really hoping for that money. I know this new role will be much better paid, but in my mind, it’s money I already earned that should’ve already been paid out. Do I ask my new employer for more time so that I can put in my notice after I receive the paycheck ? I’m scared they won’t like that as a first impression. Or do I just put in my notice and hope for the best? It is a 12 person firm, so my understanding is that certain labor codes may not apply to them. Am I just out of luck? If not, how do I phrase that email to my new employer?

Any advice would be much appreciated 🙏🏻

Update: My new employer let me push my start date out by 2 weeks, so I’ll put in my 2 weeks after I get my bonus. I appreciate everyone’s insight and help! When they gave me my offer they were pretty firm on the 2 weeks, but I’m glad they came around. All I really wanted was my bonus so I’m fine with it 🤷🏻‍♀️ thank you!