How to correctly handle Rx2 delay when receiving a long msg in Rx1

I’m implementing a LoRaWAN class A layer, and something is not 100% clear from the standards.

There is a 1 second delay between the start of Rx1 and Rx2 receive window.
On the other hand, with low datarates, I think it is possible that receiving a message can take longer than 1 second.

So how do you correctly handle the case when you receive a msg in Rx1 (could be for our device, or for any other device) and the reception takes more than 1 second…
It’s only after receiving the msg that we can determine if it is for our device, and if not, we should open Rx2, but it is already too late for that…

Should we examine the msg while it’s being received, and abort the reception of the header tells us the message is not for our device. I think this would make an implementation much more complex.