Join in mid December or early January?

I have an offer from a late stage start up. I've to give a start date with them pretty soon. Given the timing I'm thinking mid December or January beginning. Below are some factors in my scenario: 1. In h1b Visa. Transfer done. 2. Contacting right now. So no vacation days here. Will not get paid for Christmas holidays. 3. No stocks or rsu at new place. 4. Any tax implications? I was part of headcount reduction earlier in the year. So already have two w2 this year. 5. Heard joining in dec can be more relaxing. 6. Any other factors in start up? This would be my first startup experience. My thinking is December. But let me know if you have any strong points for January if I'm missing anything. Thanks in advance.