If you have to purchase the jersey- you choose when it wear it.

However (and this is rare in NZ) if the jersey is part of the entry fee and everyone gets one and it's handed out before the race, the I have found it is expected that you wear it on race day.

However I do agree, I only wear items pre-tested/that I know. Also you might want to wash the item before wearing as well.

It does look great when everyone wears the same jersey photographic wise, but it can be really hard to tell people apart as well!

I was selling some cycling tops the day before the race at "pick up your race packs" expo and they sold like hot cakes (very cheap). The next day I was amazed at how many people wore those jerseys to do the cycle race- did they not have a cycle top at all to wear when they arrived and wear just going to wear a T-shirt?