I call BS.
I have 39w ATI Purple Plus and it, like all T5's, fires instantly.
Try swapping in a different bub or moving the bulb to a different ballast to rule out a bad ballast but I'd say probably a bulb issue.
It's tough to tell with T5's unless you have some way of measuring light ouput such as a PAR meter.
Depending on daily use, 12-18 months should be the minimum.
Watch for shifts in colour spectrum, light intensity, undesirable algae growth or slowed coral growth all of which may be an...
I have a medium on my 65 gal and the chaeto grows well. I've also got some caulerpa racemosa in there, although not be choice, that grows ridiculously fast along with a 3" sand bed and some bits of rock rubble. I'm sure it does help to control nitrate and to some extent phosphate, but more...
You shouldn't need to with quality bulbs, but you may want to for added flexibility.
I run 2X250W Hamilton 14k with 4XT5HO (UVL SuperActinic, Purple Plus and 2XHamilton Actinic.) I use the T5's for dawn/dusk and find the Purple Plus gives my reds/pinks a nice pop.
If you've got the room and...