wrist exercises at different time as HS work?

Is it ok to separate the wrist exercises from the actual HS work (exercises in the morning and HS work in the evening), or must they be done together?

Generally,  doing them separately is better than doing nothing. 

Personally, I prefer to keep everything together as I find the combination of wrist stretches and wrist exercises to be a nice warmup for the handstand work. 

I would say it's OK to do what you're saying, but it may not be the most effective training method. By the way, it probably takes me about 7-8 minutes to do all of the wrist work. Combined with one HS PE you're looking at less than 20 minutes even if you're dawdling.  So unless you're doing a ton of accessory work or you're the busiest man alive I would suggest just keeping them bundled. 

I consider them a sort of Pre-skill work in case of handstand. so basically they are better if done before.