Please let us go a THREE DAYS' JOURNEY into the wilderness, that we may sacrifice to the LORD our God

[TonyChanYT]

God said to Moses in Exodus 3:

18b "You and the elders of Israel shall go to the king of Egypt and say to him, ‘The LORD, the God of the Hebrews, has met with us; and now, please let us go a three days’ journey into the wilderness, that we may sacrifice to the LORD our God.’ "

Did God instruct Moses to lie to the king of Egypt about taking three days?

No. It merely said that the journey into the wilderness would take three days. Keil and Delitzsch explained:

Was it the case, then, that the delegates were "to deceive the king," as Knobel affirms! By no means. God knew the hard heart of Pharaoh, and therefore directed that no more should be asked at first than he must either grant, or display the hardness of his heart. Had he consented, God would then have made known to him His whole design, and demanded that His people should be allowed to depart altogether. But when Pharaoh scornfully refused the first and smaller request (Exodus 5), Moses was instructed to demand the entire departure of Israel from the land (Exodus 6:10), and to show the omnipotence of the God of the Hebrews before and upon Pharaoh by miracles and heavy judgments (Hebrews 7:8.).

God continued:

19 "But I know that the king of Egypt will not let you go unless compelled by a mighty hand."

The king of Egypt would not even agree to this basic request. God would show him more of His cards as events unfolded over the next several chapters.