Dude, seriously don't worry about it. I actually used to think that you should avoid cardio and energy system work at all cost when doing the layer system. But...
A lot of football used it while also doing pretty intense metabolic conditioning twice a week and got super strong.
A lot of hockey players did the same but with 2 metcon sessions and 1 ice practice per week and also got very strong.
I am doing metcon challenges/energy system work myself and my strength is going up.
The only thing is that if you want to keep on adding more strength and size you might have to increase your nutrients intake a bit.