Time machine back up frequency and impact on computer speed

I have two MacBook Pros wirelessly tied into a new 2T Time Capsule. The backup are NOT working well and when they working (orten at the same time) the computers (especially internet) slow down...
Is there a way to reduce the frequency of backups or some other way to stop it from creating a problem... I am surprised that this feature does not exist in the set up for the time machine.

This might help though I have not used it personally others have. I suspect each Mac would need a version of the software with the intervals set so that only one backup occurs at a time. TimeMachineScheduler - set the backup interval of Time Machine

As mentioned I use a different app, TimeMachineEditor, but they both accomplish the same thing. I really don't need hourly backup's of what I do, so I have mine scheduled to back up just twice a day. The app that Slydude suggested has the advantage of giving you control of the hours, looks great to me.