2 - 5 minutes
Needed to replace iPhone 4 battery and also put on the revelation back cover.
The experience went well. The battery was indeed stuck down with much adhesive, so keep prying and it comes out. The tools were useful. All in all a good experience.
It's not hard really. Just keep prying at the battery!
Metal Spudger Set
SIM Card Eject Tool
iFixit 6 Inch Metal Ruler
iPhone 4 Revelation Kit (GSM/AT&T)