I don't see how it is in the OM's interests to support this plan. What makes you think he will not sabotage it? It is interesting how the tables are turned in a triangle - the OM thinks YOU are holding her hostage? You are her husband. I am so impressed at your faithful love for her.
I am currently reading "Surviving an Affair" by Harley. He recommends cutting off the affair immediately forever if possible. But he says it is six months to become free from the addiction, with no contact during that time, and even one sighting starts the clock over. I don't know if I was you, if I would skimp on the time part of the request. Are you afraid if you ask for too much, your wife won't agree? Six months is a lot less than 21. Five weeks is a very short period of time. I encourage you not to short-change your opportunity for dedicated time together. I believe your wife wants to come home, and she needs your help to get disentangled from a very addictive OM.
By the way, in this book I am reading, in order to ensure compliance with no contact, the phone number, e-mail address, everything is changed. The spouses agree to this together. And there is an agreement between the spouses to check in each day to confirm whether there was contact with the OM. If so, you say thank you for being honest, and you discuss what further precautions are needed, and the clock starts over. It seems like you might be able to negotiate a longer break and be very clear about the boundaries during the break - and if your wife agrees, because she wants to give the marriage a chance, then you are supporting her wishes and protecting her needs too.
Just my thoughts.
PositivelyListening ************************************** When one door of happiness closes, another one opens; but often we look so long at the closed door that we do not see the one which has been opened for us. - Helen Keller