An advanced version of the time manipulator that allows you to decrease the rest timer of any given action by 1hr up to a maximum of half the original time. This could be a rare drop, lvl 7+ base reward, or even a GP item.

+0.5 this way is waaaayyy to op. However, as a drop from lv. 7+ bases, and decreases your CURRENT invasion and ability timers by half, it'd be good.

I'd feel more comfortable if it was a times repeatable mission.

Killing level 7 bases is a higher rank thing.
Some groups kill more level 7 bases than you might think.

Actually like the mission idea. Maybe make it a repeatable like the purger mission but make it a daily so that you couldn't get 50 modifiers in one sitting.

An advanced version of the time manipulator that allows you to decrease the rest timer of any given action / ability by half the remaining time. Legion mission task completion drop. (legion mission timer not included).

make it a repeatable daily mission that uses 15 TM per completion

I agree with the principal, but it should take more than 15 TM's per completion.
Something like 250 E and 1 TM, 25 times per completion.