It's difficult / impossible to judge without having been on your shoulder, as every situation needs to be handled differently. However, I think that you might be moving early if there is time for a van to overtake even after you've had your arm out for ages. I'm not saying / can't say that for sure, just suggesting that you might want to cogitate upon the timing.
The other thing, and I know it's contentious as it has been discussed here before, is that I (nearly) only signal if I am changing speed or course. Moving around within my lane is neither so I will very rarely signal. It's something that I was taught during my motorbike test and has been reinforced in advanced bike training, from the police, the IAM and private tutors. That said, of course, I move faster on the motorbike than I do when cycling, so I do understand the circumstances are not the same, but I still very rarely signal to move within my lane.
Lifesavers, though, I do them lots.