I have an office job and can spare 10-15 minutes between calls, some afternoons.
I would like to make use of this time by learning or practicing things that may help with my guitar playing.

The first thing that comes to mind is practicing my scales. I am currently learning the 5 shapes of the Minor Pentatonic scale, so this would be a great thing for me to practice at the moment.

Any other things I could work on whilst I am sat around my desk?
Try to practice things that have multiple benefits - scales, arps, finger independence exercises are all good.