Wireless UART Speed Shift
If your data is infrequent bursts, then you should be able to resend it at a lower data rate, using any micro controller which has two UARTs and enough memory to store an entire burst.  You could probably even do it with some tiny single-UART parts by bit-banging the slow side.

As long as you can resend on the slow side before new data comes on the fast side, I don't think you should have any problem.  And your delays should be deterministic within a few clock cycles so you may not need the timestamp (or does that wireless link do resend on error?)