Sticking some anecdata in here..
I had a hole that wouldn't seal. Glass-strewn cycle path in Gateshead. Plugged it. Didn't have the right glasses on, couldn't see properly. Re-plugged at home. Seemed OK. Didn't hold pressure overnight - time to GAMI. Shop topped up sealant, all good, but recommended a service (hmm, income generation, surely not) and said if I was planning on 'events' rather than just riding, perhaps changing the tyres would be prudent. Recommended Spesh Roubaix.
Service duly booked, bike not ready to collect 24 hours later.. Tyres not holding air. "we've had this before with these tyres" WTF, why did you recommend them then...!
Anyway, they don't want to send it home till it spends a night without a massive pressure drop. I guess if I was DIY I'd do as recommended upthread and take it for a ride to settle the sealant in, and they're not likely to do that given that the grease monkeys are big 6 foot blokes and the bike is XS.