It depends. In particular, it depends on your customers.
The absolute best thing you can do is to set a company-wide update day, so your customers are not left in the dark in the event that you did a software update.
For us, we update on the 15th of every month (unless something urgent comes out), and we put an announcement up about it. It is a balancing act to keep a regular flow of updates, ensure that you're not breaking clients' stuff, and making sure that you are keeping clients in the loop without bothering them.