John Gill 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)

And Moses said unto Pharaoh, glory over me
If you can; take every advantage against me of lessening my glory, and increasing your own; or vaunt or boast yourself against me, as the phrase is rendered, (Judges 7:2) (Isaiah 10:15) or take this honour and glory to yourself over me, by commanding me, and fixing a time to pray for you, and I will obey your orders; which agrees with the Septuagint, Syriac, and Vulgate Latin versions, and the paraphrase of Onkelos, "appoint", or "order for me"; that is, when I shall pray for you; or do me this honour, to believe me in the sight of the people, to declare before them that you believe that upon my prayer for you this plague shall be removed:

when shall I entreat for you, and for your servants, and for your
people, to destroy the frogs from you and your houses, that they may
remain in this river only ?
Moses agreed to entreat the Lord for him as he desired, but leaves it with him to fix the time for doing it; and this he did, that it might appear that the removal of the frogs, as well as the bringing of them, would not be owing to chance or to any natural cause, but to the Lord himself; and though Moses had no direction from the Lord for this, that is recorded, yet he might presume upon it, since he was made a god to Pharaoh, and had power to do as he pleased; and also he knew the mind and will of God, and might have now a secret impulse upon his spirit, signifying it to him; and besides, he had the faith of miracles, and strongly believed that God would work this by him, and at whatsoever time should be fixed.