I think it is more than ok to ask for this, it is what you need.

I needed to tell my T about a very difficult subject that had suddenly resurfaced after being in hospital. I wasn't sure that I could say what I needed to say, but knew I needed to get it out. I told my T that I needed to tell him something that was going to be hard to say, especially as I did not know what his reaction would be, and asked him to please just give me time so that I could start to tell. He did, without issue. It was one of the first times I asked for what I needed in therapy.

It worked out well and I am sure it will for you too.