Why did the Thought Police wait so long?

I was reading-up on 1984 in forums and came across this question. Whilst I found it facinating, the answer caused even more intrigue. User 'Duane' stated the following:

Oh, goody, this is just begging* for a Doylist vs. Watsonian analysis...

The Watsonian reason is that the Thought Police wanted to study their victims like bugs under glass. Remember, the Thought Police agent lied to Winston when he told him there was no telescreen in the room he was renting to them. So they were already planning to monitor them with a hidden telescreen. They want to watch the deviants and traitors "in the wild", in order to learn about them so they can hone their skills of totalitarian oppression.

The Doylist reason is, of course, Orwell needed the delay in arrest so he could get write about Winston and Julia's thoughts and secrets and build up total empathy for them before beating them to a pulp...*