I know if you play a players P for 90 minuted he uses 1 EL
what happens if the guy only plays for 45 minutes ? does he still only gain 1 ?
or does he gain 2 back ?

Passive for 45 minutes will use 3 EL and gain 4 after game. So +1

Passive for 54 minutes is SAME, so here is the math(s) or arithmetic.

90 / 5 = 18
18 * 3 = 54 minutes.

Same way if you play dirty ar aggressive, you see subs at 51 mins or 64 minutes sometimes. Best use of EL.

so no use in played a guy who is only going to play for 45 minute P because he uses the same amount of EL as when he plays Normal

pretty much.

Lesson learnt!

Learnt? Perhaps a grammar lesson is next up for GM boss!!