Frequency Hopping 900MHz -- Noise Floor Mitigation and Algorithim Design
You can send a short packet on a beacon frequency once a second or so and hop through the other 59 frequencies with payload on a predetermined schedule.  The short beacon packet has the current position in the hopping sequence.  

If you want to implement a "cognitive" system, you can look at the noise floor across all frequencies on the main transceiver and send a mask indicating which frequencies will be used in the hopping sequence in the beacon frame (you will need more than 60 total frequencies so you can skip high noise channels).

This scheme requires the use of a single, unchanging beacon frequency, but you can design the system to have secondary beacons on a variable frequency in the hop sequence.  This will give you one second lock-on as remote transceivers are connected to the network and no additional latency for transmitting once you have acquired the sequence.

If you have multiple transceivers and need to allocate timeslots for remote transmission you'll have to design this into your protocol.  If you provide information in your question on the number of transceivers, frequency of packets, etc I can refine this answer to your particular situation.

If you are occasionally sending a single packet from/between a large number of remote stations, LORA is probably a better solution than building something from scratch.  LORA has an extremely high link budget, so you will probably be able to meet your range goals without going over the 250mW regulatory threshold and using external PAs on your transceivers.  In a suburban (high noise floor) environment we achieved >1 mile range (LOS) with Semtech LORA transceivers without external PA (but with a decent antenna on each end).  Note that some of the Chinese LORA boards are terrible (mostly low tolerance crystals, but also generally bad RF layout).