Even when buying the battlepass, how much would you have to play to earn every unlock in a season?
It depends. Just completing the weekly challenges only nets you 55 tiers/100 and early on you get levels quite quickly (especially if you play with friends who boost your exp, even easier if you win regularly with said friends). Weekly challenges probably won't take more than 2-3 hours per week if you really focus on them. I'd say 65-70 levels can come somewhat efficiently if you just do the weekly challenges & get some levels in the progress. Past that leveling up even a single level becomes much more of a grind (you have to win, like, 7-15 games for a single level even if you have friend EXP boosts helping you out). So you're left with having to get about 30 levels past the battle pass challenges & the levels that you can probably get going for them. Daily challenges give you 0.5 levels per day and you can have up to 3 daily challenges queued up at once, so that's 1.5 levels every 3 days. 3 levels every 6 dailies, so 30 levels in about 60 days/daily challenges. Since you can queue them up, you don't have to play every day but you DO have to log in on 60 days. This can be done on your phone or Switch if you don't want to boot up PS4BonePC every day, if you really want to spare time. :P
If you want to be as efficient as possible, early on in the season you could just focus on doing daily challenges every 3 days, since if you let 3 dailies queue up, it's likely that you'll get something done towards completing every one of those 3 daily challenges in every round if you focus on the challenges (like, instead of playing & completing them daily, you can get shotgun kills, open chests & ammo boxes and outlive opponents all within a single game vs. opening chests one day, outliving opponents for 2-3 games another & killing people with shotguns the next). After a few weeks, you'll probably have some of the more generic weekly challenges done even without trying to do them. Once you've got a few weeks of weekly challenges stored up, you can start doing the more specific ones and finish challenges more efficiently within single rounds of BR, much like the dailies. So that can cut down on time needed for weeklies dramatically.
Ultimately the most important thing to get to battle pass tier 100 is to do enough daily challenges. You can tidy up whatever weekly challenges you are missing within the last week or two quite efficiently but you have to do about 60 daily challenges if you don't spend a lot of time grinding for levels. If you do them as efficiently as possible, you have to play maybe an hour or hour and a half every 3 days to empty the queue for the next few daily challenges, so that's maybe 20--30 hours of playing just for dailies. Weekly challenges can depend on your skill level, how aggressively you go for them in each game and a bit on luck (i.e. if there are some "kill people in X location" challenges, whether you ever confront enemies in some of the less crowded landing/visiting spots). A "Kill 5 opponents with a shotgun" challenge can be achievable within a single game if you luck out on and/or are skilled enough OR it can take 5-8+ games. But, again, it's not as time-consuming if you have weeklies & dailies queued up, so even if you don't get a shotgun kill in every game, you'll probably get SOMETHING done (especially if you go out of your way to visit a target location or do some more specific tasks).
2-3 hours of playtime for weekly challenges (or less) x 10 and about 20-30 hours doing 60 or so dailies through the season. I'd say 40-50 hours of playtime within the 2,5-3 months that these seasons usually last is probably the bare minimum if you want to do everything as efficiently as possible & focus on getting something done in every game & don't play any more than necessary. But it can balloon up to a lot higher a number if you don't focus on them and do them inefficiently.
