This will depend wildly on how much practice you have and what the question is, it's not uncommon to spend an hour or two on a question at the very beginning, especially on the longer challenging questions. However, as time goes on you should find that you can often do some of the questions that have shortcuts in 15-20 minutes, however that's non-standard. Standard advice (which I disagree with, FWIW) is that you're doing good if you can do a question in 45 minutes. Personally, I feel that 45 should be replaced with 30.

But yeah, hour or more at the beginning is nothing to worry about. In fact, I'd suggest not caring about the time taken to do questions just yet, that's something you can worry about later. The important thing right now is just being able to do questions, no matter how long they take. STEP is meant to be hard starting out and with enough practice you'll bring that time down drastically. Remember also that in earlier years, question difficulty is a lot more varied, so some questions might be overly long and others will be overly short.

I would argue that sometimes questions with tricks you don't spot can take a lot longer than an hour or two. Indeed I remember staring at a few questions over several days. With STEP problems (and also with university mathematics), sometimes it's worth leaving a problem for a day or two if you've been stuck for a while and then coming back to it and see if you've managed to gain any inspiration. I've found that solutions have sometimes come to me when I've been least expecting it.