Update: after riding the bike a lot of the past few days, the leak rate has slowly subsided to about 5 PSI / 24 hours. It appears that the LBS's "advice" to ride and spin the wheels so that the sealant had a chance to spread out and plug the little backs and holes was correct. Still, it should not have taken almost two weeks for the tires to stay inflated overnight. I attribute it to the low-budget rims that came OEM with the bike. Thanks for your comments.