Questions about spawning hitboxes

In a platformer I'm designing, I have a few animations for attack. Some 3 frames long, some 4. I was wanting to spawn hitboxes at certain frames in each attack animation. Each of these hitboxes would then, on collision with something in the enemy family, add to it's damage private variable and push them back a x amount of pixels.

I was wondering how would I tell the hitbox to spawn only during certain frames?

You could try to store your animation frames in variables.

Then ie. if private variable 'animation frame' = 5 spawn your hitbox.

There's a condition to compare frames.

Also cant you just alter the collision mask?

Have you seen UberLou's fighter tutorials? There is some really great info on hitboxes in them.