You can, you just restart the 24 months contract period.

For those having wifi issues with DIR615, you might want to try resetting the router to defaults and reconfiguring it. My router stopped providing any network access to wifi clients after some time requiring a reboot to fix, it got worse until it'll stop working less than 3 minutes after reboot. Decided to reset to default and try again, so far after >24 hours wifi is still working properly.

Mine was done in about 5 hours. About an hour from outside to my computer (I'm just a few metres from the TM pole) and 3+ hours to wait for TM to set up signal to my GPON modem.

Why not refer to the piece of paper which came with the DIR615 router? It should be admin with blank password.