well the problem with time zones is that not every station airs the show on the same night or time even.
here in montréal, we get charmed on sundays at 11pm on Fox44 (tri state area) however the WB airs it at 8pm.
so you see, airtimes don't or shouldn't matter. besides you dont see the "time" anywhere on the home page. so if it where me, i'd just use the function to tell me the name of the day the show airs and leave it at that.
time calculations are impossible when you dont know the air times for each channel. so its just a guess and not an educated guess since you don't know the time it airs for every member here.
so perso i 'd just go for the date not the time. and people will understand and not care.
as for availability i think you mean tor, well i just leaved tvtad on or rather µt with its rss feed and i'm good with that.