I think the problem with the gel and roses is if the heads are touching the gel, the petals can go soggy pretty quickly (unfortunately baccara are the worse for showing up water damage) I think if you are doing them on the morning they should be fine, i'd worry about them if you made them any longer in advance though. Sarah's given good advice, do a practice run first!.

Its always the people with a small budget that are the pickiest, i've never had to do a mock up though- think I must have the gift of the gab! People who are that picky make you too scared to add any extra "designer flourishes" you may think will look good as you're making the designs, which means they'll get less of a service in the end because they've put a dampener on creativity!