The quote/question literally translates
lord, if/is* in the time it, will you restore the kingdom of Israel?
*while εἰ does not mean "is", it functions similarly as "is" in this context
However, εἰ can have a slightly different meaning when it introduces an interrogative clause:
εἰ, if: but in strong statements, approaching oaths in character, and as the first word in an interrogative clause, it is probably a mere graphic equivalent, first appearing second century B.C., of ἦ [and should be written εἶ], and in the former case = verily, indeed, assuredly (sometimes negative [Semitic], assuredly not, Mk. 8:12, Heb. 3:2), while in the latter it is merely a particle asking a question. [The Latin translators, however, rendered interrogative εἶ by si.] εἰ μή (nisi); but only, e.g. Lk. 4:26 f., John 15:4, Ac. 27:22, Rev. 21:27; in Mk. 6:8 probably due to a misreading of an Aramaic word = and not: εἰ δὲ μή, εἰ δὲ μήγε (Aramaism?), (alioqui, si minus, sin autem, &c.), otherwise: εἴπερ (= εἴ περ) a more emphatic εἰ, if indeed.
(Souter, A. (1917). A Pocket Lexicon to the Greek New Testament (p. 72). Oxford: Clarendon Press.)
Lexham English Bible translates it as "is"
Is it at the time (LEB)
NKJV just drops the word and makes "at this time" an adverb clause
will You at this time
The word, in this case, introduces an interrogative clause.