Piece of cake. Open the DFS Management snap-in and add your replication group to the display if it's not already there. You can right-click on the group and there should be an option to
Edit Replication Group Schedule.... Select that and you should be greeted with a dialog that looks like this:
You can click on individual cells or click and drag over a group of cells. Then, change the
Bandwidth usage: drop down to
No replication. Alternatively, you can click the Details button and edit the schedule using that interface as well.
Edit: I should also mention that you can set the schedule on a per-connection basis rather than globally for the whole replication group. When you have the group selected in the DFS Management snap-in, switch to the Connections tab and open the Properties dialog for any of the members. It should have a Schedule tab that is normally set to the group's schedule. But you can set it to a custom schedule that will only affect that connection.