Why does it take 20-30 seconds for a fluorescent tube to start?
If you have a starter, that is definately bad. Starters are cheap and easy to install, I can't remember the last time I have seen one. (Electronic ballast don't use starters). Since the lamp appears to be bright the ballast should be good. If there is no starter I would look at the ends of the lamp, the other thing that kills fliorescents is the electrodes have been eaten away inside the tube (the lamp ends are usually very dark when this is the problem) but it looked very bright so go for the starter  - they do wear out, I used to keep a box of them handy.