Spraying the pulleys will only make things worse. It's slipping which is causing the problem, and lubricant will only make things worse. Even if it does cause the squeaks to stop, it could also cause improper function of the offending accessory, who's pulley is causing the squeaking.

Instead of trying a bandage solution which will only make things worse, you should rather try to fix it appropriately. Although you may be tempted to wait this out as this sounds very much like a humidity/water problem. As you say, it occurs after the car has sat for about 4-5 hours (lets the engine cool down completely), and then stops after the first 5 minutes (after the engine evaporates the water).