Maintenance for the week of November 25:
• PC/Mac: NA and EU megaservers for maintenance – November 25, 4:00AM EST (9:00 UTC) - 7:00AM EST (12:00 UTC)
• Xbox: NA and EU megaservers for maintenance – November 27, 6:00AM EST (11:00 UTC) - 9:00AM EST (14:00 UTC)
• PlayStation®: NA and EU megaservers for maintenance – November 27, 6:00AM EST (11:00 UTC) - 9:00AM EST (14:00 UTC)
It's not dependent upon whether or not you actually use the skill (Unlike TES single-player games). Skills increase in rank as you gain experience and they're on your hot-bar, regardless of whether or not you actually use them in battle, or otherwise.
If you run around all week killing trivial enemies and using it - or any other skill - they will not change in rank one bit.