Time Dialation is best used to extend a single target card which (in 4man content) should be your go-to in terms of cards. Theoretically an AoE card seems to march up at first in terms of people buffed (50% × 4 people = 200% like Extended would) but when you look at it that way you're weighting tank and healer damage being buffed as being the same as a buff on a dps which shouldn't really be the case.

I get that sometimes the dps are really weak, more than once I've found myself Enhanced Balancing a WAR because it was the best option available to me, but in general dps should be doing considerable more damage than you or a tank. For dungeons what I look for as far as performance indicators of a good dps is basically are they properly AoEing and are they tossing out their utility abilities. Most people who do those things are going to be worth single buffing because they probably know their role.

In short - for a dungeon/light party setting you should shoot for Extended cards first (Balance > Spear > Arrow) then Enhanced and Expanded should kind of be a last resort. This is due in part to proper use of time Dialation really increasing the card uptime on DPS.

You shouldn't be afraid to extend regens on a tank (though if you're going to do so might as well load them up with both regens and potentially even the one from CU and maybe even the Largresse'd versions) but it also shouldn't be your primary goal with Time Dialation in terms if efficiency. Saving yourself one GCD reapplying Aspected Benefic is almost always lost potency when compared to what a dps could do with extra time on a Balance.