index.html.in: set ticket expiration to 90 minutes

index.html.in: set ticket expiration to 90 minutes

This is what CharmPass does for one-way tickets, and the expiration
date/time only blinks for about ten minutes after you use a ticket in
the official app. This is a tiny detail (and we could always ditch the
blinking to make the display accurate with an expiration of 1h) but
it's easy enough to get completely right, so why not?