Is it possible to get hired at a regional and fly Sunday through Thursday, avoiding Saturday? Would the scheduled possible Saturday days be possibly traded, or if necessary called in as a sick or vacation day? Could this plan work at the majors as well until you get enough seniority to make such a plan possible with regular scheduled line flights?
Unfortunately that’s not going to happen. Saturday is the weekend and since most people like their weekends off they go senior. While you can sometimes trade them there’s no guarantee. Most airlines don’t allow you to break up you vacation weeks into separate days (plus you don’t get any right away) and if you call in sick every Saturday your first year on probation there won’t be a second year. Besides that to be an airline pilot you must have a certain amount of flexibility. Even if you could secure every Sat off on paper, this is aviation and there are often problems. You could very well be scheduled to finish your trip Fri afternoon (hours before sunset) but inevitably there will be weather or maintenance delays and if you started the trip you have to finish it. In short the airlines are not Shabbat friendly, unless you move to Israel and fly for El Al.