An excellent idea. Travelling back through time, you arrive at the building to find it completely deserted – no Daleks, dangers or even the bucket of cleaning supplies. Plenty of time to prepare.
Working quickly, you’re able to fashion a transmitter that will excite the molecules of the Dalekanium armour, blowing them up and disintegrating their remains as soon as the timer finishes counting down. You set the timer to go off the second you left in the Tardis earlier, so everything should go together smoothly – past-you flies away, the transmitter goes off and the Daleks are toast. Lovely.
You’re still a little confused as to how you ended up in that room or why the Daleks were here in the first place, but hey – that’ll probably be resolved in the season finale.
Now, there’s only one thing left to do…