So if they don't respond to your "do you have time to talk" initial message, then you just don't invite them to the concert at all and never tell them about it?
All to avoid just asking them up-front whether they want to go or not?
That's wild, I genuinely don't understand how this is better in any way.
Imo if the question is urgent, either call them or add something to the text like "tickets are going quick and I'm going to buy them ASAP, so if I don't hear back by , I'll assume you're out"