How to Throttle Backup Speed when Taking Backup over WAN

Hi All, 

I have a few backups that run over the WAN . They run at a fix time and often we have to suspend them in Business hours because that imacts overall performance.

I want to be able to do the following 

1. Backups should run at a speed that I specify so that the line does not Choke.

2. It would be extremly if I can tune it according to the Time. ( For Ex. If the Backup stretches beyond 8 AM ie the Office opening Time, the Speed should go down so that Office network is not impacted

Is any of it possible ???