Does a divorce restricted by a future time—with two previous, clear divorces having occurred—take effect, and what is the legitimate religious ruling for dealing with this situation, especially given that there are multiple jurisprudential opinions concerning it?

Your statement to your wife: "You will be divorced in the sixth month," is a promise of divorce and does not result in a divorce by scholarly consensus. As for your statement: "You are divorced in the sixth month," this is the pronouncement of a future divorce. The majority of scholars hold that it does not take effect until the stipulated time arrives. Therefore, there is no harm in enjoying your wife until the appointed time, at which point she will be irrevocably separated from you if this is the third divorce.

It is possible to circumvent the divorce by resorting to Khul', and this is the view of some scholars who consider Khul' to be an annulment (faskh (definition)) and not a divorce (talaq (definition)).