Replying to Importance of leg day

I'm still learning to slide my first rails and hit my first jumps, so I'm just wondering about the importance of regularly having leg day/how often it should be done. I run a decent amount but i have chicken legs (my quads are normal but my calves are pretty small). i also work out my upper body to somewhat get past my general scrawnyness.

I'm hoping to make it as easy as possible to scissor, rotate the full 90 on a rail, 1s/3s on smaller jumps and other simple stuff.

I probably wouldnt be asking this question if time wasnt an issue, but I'm starting college soon and the time I'll have in the gym is probably going to be less than what ive had so far. Help me out w some advice, exercises, etc.