As others have said, what you can hold is very much dependent on what type of pairings the company builds. Considering your in-seat seniority percentage, you will most likely not be able to hold anything other than 4 day trips in the initial bid if ASA continues their usual trends with pairing construction once they have control over XJT's schedules. You'd have a better shot at it with PBS, but almost certainly not with line bidding.

Part of our PBS LOA states that only 60% of pairings can be 4 day trips; however, this is TOTAL PAIRINGS and not percentage of complete schedules. Let's say the company wants to build 60% 4 days and 40% 2 days. We'll keep the math simple and say 1000 pairings are available for your seat and domicile. Of those, 600 are 4 days and 400 are 2 days. Twice the amount of pairings are needed to build a complete schedule with 2 days than 4 days. Each person bidding 4 days is awarded one 4 day per week, which will make 150 schedules. Each person bidding 2 days is awarded 2 pairings per week, which makes 50 schedules. In reality, 60% 4 days still equals 75% or more of the schedules and this number increases when you consider CDO pairings and day trips. Granted, this example is dumbed down significantly but shows the principle of the 60% rule.

That's not to say that ASA will not change their ways, but I doubt it. They love 4 days and will continue to love 4 days for the foreseeable future. At least with PBS, you might be able to snag a few 2 days or CDO's in your initial bid run instead of getting a schedule of just 4 days as you would with line bidding. You can then swap the remainder of your trips with CDO's and stuff in open time.

I want to reiterate that the PBS system has NO EFFECT on whether or not you can hold 2 days. Its completely up to what the company builds for pairings. Generally, people are holding better schedules with PBS than without. In your case, you'd be better off with the PBS system.