when getting a divorce, do one spouse have to give the other his share of 401K right away or till he or she retire???

Usually a QDRO is filed (Qualified Domestic Relations Order) and there are rules about when the receiving spouse ("the alternate payee") can or will receive his/her potion of the benefits. If someone wants "his share" right away, then sometimes the spouse who is in the retirement plan keeps 100% of the retirement plan but transfers the other spouse some other assets  or takes on additional debt payments to make up for not having to transfer part of the retirement.