If you want to know whether you can travel to chutz l’aretz during the zman, I'll say like this. Firstly, it is extremely important when in yeshiva to have constancy, a type of hasmada. So that means that having a zman where you're here for half of it, travel to chutz l’aretz, then another half - even if time wise there is not much of a difference, it really is not the same thing as having one full amount of you being in Yeshiva consistently. That's a different poshut; everybody knows that. Because of that, we take it seriously. 

If somebody wants to leave in the middle of the zman, generally it's something that that we'll say no to unless it's for a very good reason. We do try and be reasonable. So, if you have a sibling that's getting married, if it's your grandparent’s 100th birthday or 70th anniversary and the whole family is getting together and your parents really want you to be there, so we try to be reasonable and take a case-by-case basis and see if it really warrants you leaving your chevrusa, leaving the yeshiva in the middle of zman and the real disruption that that creates. Is it worth it? Or not? Is that your mitzva to do or not? Otherwise talmud Torah, that's the mitzvah; you are in yeshiva for a reason. And that means you're going to have to sacrifice on some level that you're not being able to do everything else. Right now, you are in Yeshiva, and that's the focus.  

Zman dates for the current academic year can be found here - https://www.bircas.org/what-is-the-yeshivas-academic-calendar/