I can't help you with your pruning times but I know from experience that box will regrow. I had made an attempt at a topiary spiral and didn't do a very good job of it. It took just over 1 year to fill back out!
Could that be another Escalonia. I have one with very small leaves like that. I'm looking at this on my phone so picture isn't all that clear when I zoom in

Hi Scottish, I didn't think it was another escallonia ... but as you can see my ID skills are pretty poor :))
All I can tell is that it looks quite different to and didn't grow nearly as quickly as the escallonias, and it didn't flower. I also have another one that has been shaped into a sort-of-ball.

Did you re-do the spiral or try something else?

Like I said pic ain't great on phone so your probably right.
Didn't bother again. I just let it fill in and I clipped it to get it more ball shaped. I'll maybe try source one already shaped but they can be expensive!!
Can I ask what that conifer growing to the left is. It has lovely colours

its not an escalonia, if it is not box it might be a small leaved lonicera.

Loooks like Box to me, but its not in need of renovation, really. If the plant has thick wood beneath those nice green leaves, then maybe cutting it back hard would be useful, just to induce new, soft growth next year which you can then keep shaped by regular clipping, even if that shape is a simple oval or pyramid, to the height and spread you want it. If the wood isn't particularly thick and is clippable, then I'd wait till growth begins and clip it back to the size you want it to be and continue to keep it in shape.

Now I'm on the 'big screen' with my specs on - I can see how ridiculous my suggestion of escallonia was :) Sorry!

Not a problem Scottish, I can't even connect to the internet on my phone! So backward ...
I only know the conifer as my "Christmas tree", I'm sure it's a particular type of Christmas tree but, like most things, I don't know ;) The colours are interesting though, the different stages of growth are different colours, I might put another pic up of it later, I should probably get it some outdoor lights too given it's that time of year!

Thanks Bamboo, it does have quite thick wood (certainly not clippable) which is what I was nervous about cutting into. But if cutting that back hard will give me new growth I can shape and keep to a more contained size that's the solution I wanted really. I assume that is a December/January job?

And thanks Seaburngirl :)

Yes, over winter anyway, whenever its not raining and you can bear to be outside in the cold!