We have always let our off the lead as soon as they ahve been able to go out, somewhere safe, they have a natural instict when they are so young to want to be with you as they are less confident when first taken out. We always called them by name even though they were inches from our feet and rewarded them, walk backwards away if they arnt walking away from you call them again and treat, yes they would want to be with/near you anyway so you are building on this "need" treat/praise all the time they very quickly realise coming to you is good.

This then serves a good grounding when they become more confident and with mine this was only a few days of going out, keep stepping away and repeating the recall always the same command, as soon as they move away shout them back repeat it as often as possible. We always found as well to step up the praise make more of a fuss and change the treat, use a different treat for this than the one you would use at home for the sit and down commands as its very important that recall is established for safety if you are wanting your dog to be off the lead most of the time which we did.

I think the earlier the better there is less chance for a pup of 3months ish to run away from you than a 6-12month confident dog.