How long to you have to wait after pouring the cement garage pad before you can begin construction on the garage?

You can start after about 48 hours since you will not create a big load in the first day or two of construction. Concrete continues to harden for decades bnut it is safe after 48 hours. Are you sinking floor plate bolts into the slap or drilling later? If you drill I'd wait until a third day has passed.

Yes ballengerb1 is correct, but it usually takes about 21 days to for the concrete to "cure". But the construction can begin much earlier.

Place the wall anchor bolts in the concrete as you pour the slab. Then just drill a hole in the subplate of your wall and slip the subplate down on the bolts, and apply the flat washer, and the nut.

For slabs on grade four days, for structural slabs,(those are slabs poured over floor voidform) one week, for suspended slabs , three weeks, concrete is usually cured fully in 28 days, after u pour your garage slab I would wait a week to be safe,oh and don't forget to water your slab like grass, this help the curing process and prevent premature cracks. Hope this helps