Saw a whole thread on a bike forum where a guy toasted his new top end by just sending it right away. I mean idk, maybe it's just me but that seems like a costly lesson to learn.
You're treating it like a gentle walk when it's more like a hard run that needs a warm-up. Those piston rings need heat cycles and varied load to seat into the cylinder walls right. Just firing it up and going full throttle can glaze the bore or score it up. Seen engines that skipped break-in burn oil forever because the rings never sealed. Isn't the whole point of a rebuild to make it last?