aslong as it's inside the synchronous process thats clocked from the system clock - you can do whatever you want. The code you posted is just a rising edge detect, and is done quite frequently. Just make sure its readible for yourself after a 6month/2 year/ 10 year break. Add plenty of coments. Write appropriate documentation..
Nothing like picking up someone elses code with obscure signal names, no coments, no documentation and having to work out whats going on from the 20 processes in the file!