How successful is a tubal ligation reversal & is there a time restriction on when it is best?

Varies: There is no specific time restriction, it works as well sooner and later. results vary with "how" the ligation was down. Generally use of clips (Hulka, Filshie) or rings (Yoon, Fallope) give the best reversals, postpartum (Pomeroy) type ligations are often also very good. Anything involving cautery ("burning") usually will give a less good result.