You can sell immediately IMO. If you've owned WAMU and/or WAMUQ for over 1 year,and you've received JPM shares, it is as though you owned the JPM shares for greater than one year. It's called carryover holding period. Your tax basis carries over as well. It's called carryover tax basis. If the stock is held for more than 1 year, favorable long-term capital gains rates will apply. Maximum rate is only 15%.
I will sell most of my shares the same day and will DIVERSIFY.
But think..you save 15% by holding 12 months and what if you were able to get JPM in the $30's and over time it went to $50? providing WAMU of course does not go back into competition with them, they will have little competition. If WAMU goes back into banking then yes i could see wanting stock in WAMU or cashing out and moving on...I just don't see that happening but no one knows.