Actually, the automatic updates are usually twice a day.
The automatic update only downloads a few KB. OTOH, the complete VPS is above 30MB (more close to 40).
The frequency for your offline computers should be in accordance to what you actually do with those systems.
If you continuously add files, or interchange files, that's one thing. If, instead, you use them almost "as-is", once a week should be more than enough.
And, if you could check any interchange of data between those 2 computers and external devices just before copying them, then even once or twice a month could be enough.