The "rule" is 5 hour travel time from your arrival airport is okay. The hotel will arrange the transportation so as long as they will give you a confirmation that shows your package includes the transfer then the hotel should know what's acceptable and take care of it for you. The Thailand PSAS website says it's also for booking Krabi PCR tests.
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You should reach out to the hotel, they'll know all the details and should be able to answer any questions.
I don't think there's enough people that have entered through Krabi that can answer your question. But if you decide to do it, it would be great if you reported back here with your experience to help others in the future.