custom font bar

i have made some custom font for my datapack
its a mana that has 72 frames
now i want to work for multi types of attacks
my problem is i dont know how to for example:
have the bar empty when a attack has been used but lets say attack one cost 30 seconds to recharge, it will refill the bar with those 72 frames to full again in these 30 seconds
then for a other attacks that takes 50 seconds to use it will use all 72 frames to recharge the bar in 50 seconds
i hope i explained it a little