time variable throttling rsync traffic

[Eric S. Johansson]

I am using rsync to back up across a VPN.  Unfortunately, every so often the 
home office miscreants drop a big block of data into the backup and that 
particular backup cycle takes many hours.  These same people also complain when 
net pipe is filled during the day.

What I need is an ability to change the bwlimit based on time of day.  Any 
suggestions as to how to do this?