Yes. In fact, it would be wrong to put a t- there, because of the preposition ag. (The same would apply for many other prepositions.)
Is that because in "Cen t-am e?" there's an "n" with the tongue in an apical-alveolar position whereas in "ag" it's "back"/in the velar location?
Just trying to make sense of the phonology behind why what happens when. Still struggling to make sense of the stuff in https://www.duolingo.com/skill/ga/Eclipsis
because it's in the dative case? what follows ag is usually straight forward, ag+an eclipses where appropriate
Google says that means "May we be alive at this time again !"
Not quite sure what that entails/implies, but okey doke...
Would you use this as an imperative (eg. "Do it at this time" meaning "Do it now!"), as a general description (eg. "We don't have any at this time" meaning "We don't have any now, but if you come back later, we might"), or in either circumstance?
Since it’s an adverbial phrase, it wouldn’t be used as an imperative. (I’d imagine that if someone intended to express the adverb “now”, anois would be used.)
No. In English, "this time" and "at this time" don't mean the same thing. "this time" means "this occurrence" ("I'll hit the target this time") whereas "at this time" refers to a point in time. You don't use ag an am seo to say "I'll hit the target this time".
"this minute" and "at this minute" both refer to a point in time, so they can be compared to ag an am seo.