If a provider is marked Available Now, and they don't respond within 15 minutes, I text my next choice. Sequential, yes, but the prize goes to the most professional. If you're available, you need to respond. I say clearly that I'm looking to hire that night, so I'm being transparent. And if someone texts back too late, I honestly tell them that they didn't respond and I've already hired the guy that did.
Luckily, a pool of regulars allows me to avoid that. However, the guys who get in that pool already proved themselves by being professional.