By the way, I thought I might as well let you know that there are several problems in the above.Quomodo efficienter mactare tempum? Studere linguam latinam.
1) Tempus is third declension neuter, so the accusative is the same as the nominative, tempus.
2) Mactare isn't used in this sense; terere is a better idea.
3) I think discere would be better here than studere. The latter is only rarely transitive; it's more often used with the dative, but then the sense is a bit broader than just "study"; it's more like "devote oneself to" or the like.
3) Infinitives aren't used that way in Latin. In sentences like "how to...?" and the like, Latin uses different constructions, notably the subjunctive.
So I would suggest to fix it to:
Quomodo efficienter teras tempus? Discas linguam Latinam. Lit. "How may you kill/use up time effectively? You (would) study Latin", or "(let you) learn Latin".
Or: Quomodo efficienter teratur tempus? Discatur lingua Latina. Lit. "How may time be killed/used up effectively? Let Latin be studied (let one study Latin)."