Albert Barnes Commentary Exodus 8:9

"And Moses said unto Pharaoh, Have thou this glory over me: against what time shall I entreat for thee, and for thy servants, and for thy people, that the frogs be destroyed from thee and thy houses, and remain in the river only?" — Exodus 8:9 (ASV)

Glory over me - See the margin, "have honor over me," that is, have the honor, or advantage over me, directing me when I am to entreat God for you and your servants.

When - Or by when; that is, for what exact time. Pharaoh’s answer in Exodus 5:10 refers to this, by tomorrow. The shortness of the time would, of course, be a test of the supernatural character of the transaction.