Can you target a creature with hexproof with a spell you control if you gained control of it this turn?

Hexproof means the permanent cannot be the target of spells or abilities your opponents control (CR 702.11b). The protection runs in only one direction: it stops your opponents from targeting it, not you yourself.

Because you now control the creature — regardless of how recently you gained that control — the creature is yours, not your opponents'. Therefore, when you try to target it with a spell or ability you control, hexproof offers no protection and you may freely target it.

The timing of when you gained control is irrelevant. What matters at the moment you choose targets (CR 601.2c) is simply who controls the object and who controls the spell or ability. If both are you, hexproof does not apply.

Concrete example: Suppose you steal your opponent's Dungeon Geists (which has hexproof) with Control Magic. On that same turn, you cast Twiddle targeting Dungeon Geists. This is perfectly legal — since you control both Twiddle and Dungeon Geists, hexproof does not prevent you from targeting it.

Note: If your opponent were to try to target the stolen creature with one of their own spells, hexproof would protect it, because they are now your opponents trying to target a permanent you control.