3rd meal on shabbos Rosh Hashanah

What is the best way to go about this? We eat very late, we pray till very late. Kind of tough to do. Is there a time we should eat the third meal no later than? Is there any time where it is prohibited to eat it anymore because you were going to need to have a holiday meal at night?

If you know yourself and your situation and you’ll have an appetite for the night meal, you can eat until shkia