I think I've seen this asked before. Do a search for it and you should find it.
Off the top of my head glutamine peptides are much more stable in liquid and have better absorption.
There are different opinions on dosage but generally, 10-30 grams is optimum.
Glutamine's most useful property is it helps for recovery. If you're taking it for this purpose, it can be taken anytime, even with your protein. Post workout is when your body really needs this stuff but thoughout the day is good too.
Take it on an empty stomach for a small GH release. In my opinion, the amount of GH released is insignificant so I don't bother with this part.