[O] Timestamp: Forward or backward by a week

[SW]

Pressing S-left/right anywhere on a timestamp decreases/increases it by one day.

Pressing S-down/up on a component of a timestamp decreases/increases it by one
unit of that component.

How can we include an easy and quick way to decrease/increase the timestamp by
one week. I find myself having to do that quite often (increase). It's not
difficult to hit S-right/up seven times, but there is the possibility of
miscounting.

Should I just bind ``C-u 7 S-right`` and ``C-u 7 S-left``?