48 hours is enough if the soreness is gone. Use that as a guide, hit the muscle once the soreness is gone either 48 or 72 hours later.
This is all controversial, there are many opinions. For example you've got the HIT types who believe that hitting a muscle more than once a week's sacrilege, then you've got others like Vince Basile who think that the best results come from working a muscle while it's still slightly sore. Best to try different approaches for a few months each and compare the effects.
I'm of the belief that recovery's key, which means waiting till the soreness is gone after which time it's good to go right back to it. Assuming as in your case that the muscles are completely rested on off days-a double-split routine can help with this.
Also keep in mind that the duration of the workout makes a difference-if the workout's fairly short but intense it should take less time to recover than a long volume workout. Long workouts aren't needed for size.
Soreness isn't an indicator of recovery.
Recovery time is a function of 'training age', training style, work capacity, nutrition, rest, and other factors. People said the guys who train with Louie Simmons couldn't possibly get stronger and recover, but they do. People cant believe that high level olympic weightlifters squat 6 times a week, but many do. Sheiko training gets people all worked up about recovery, yet somehow it's produced some of the strongest people, ever.
Some bodybuilders swear by their high volume high frequency workouts, training 6 days a week, hitting 'body parts' 2-3 times a week.
From personal experience, 48 hours is about right for a novice. Full recovery could be weeks for someone at an elite level. However, how you can still train while you are recovering as part of a well planned program. Also from personal experience, increasing work capacity reduces DOMS.
