Just as a point of information, my recent transfer of Membership Rewards points to DL took only a couple of hours from linkage of a new account to deposit of the MR points in the newly-linked DL account. The offiicial MR stance is that it can take up to five days to link to domestic airline accounts and up to two weeks for international accounts but in my experience it has never taken more than one day for the entire process. I assume your MR account is already linked to your DL account so the transfer should be almost immediate and well within the 48 hold of which you speak. Of course, YMMV