Actually
Spoiler:the reason why you want that mask becomes clear later on in the game, because you will need it. But I agree, the way it is now is that the game wants you to get the oil before day 3 can end, so you are right, in fact it seems at the at moment of day 3 that you need to pay 100 dollar for some oil...the timing is a bit off...
Funny that I never really noticd that until you brought it up...