Quick question- When a driveshaft is lubed, does the grease take a while to work it's way in and do it's job?

I had the lube job around 3:15, and drove about 2 miles to work from there, still hearing the noise. Drove about 2 miles back from work around 8:30, still there. Drove about 10 miles to go see a movie tonight and it was still there on the way, and even in the parking lot after the movie got out around Midnight. I drove about 10 miles home again and now it's completely gone. I turned off my heater and stereo and opened the windows because I couldn't believe it, but the noise really is gone.

I'm not too excited yet about this, because it has subsided before, only to return worse. The only way I'm thinking it will stay gone is if it were simply that the drive-shaft needed lubrication and it took driving 15 miles after the lube job for it to work. If that's the case I'm going to be one happy camper... I mean come on, how often is problem literally fixed for free at a shop?

So that's where I'm at. Thanks again to everyone who offered some help. I'll keep you all updated.

More info about noise (as requested)-
Related to vehicle speed
(Pitch of squeal never actually changes, just becomes louder)
If vehicle is stopped, engine sounds strong and clean, even at high revs
Completely stops under 24-25 mph
Has no effect on driveability
Is worse after a car-wash (washed it today with the undercarriage wash and it was really bad immediately after)
Comes from somewhere in front of and below me
Braking has no effect
Turning seems to have an effect, but since I normally slow down to turn it's hard to say
Accelerating makes it stop, but as soon as I let off, it returns

...that's about all I can think of. If it comes back is there anything else I should be listening for?