You can use your discretion but it is supposed to be from the start of the feeding.
Beginning of the feed x
My lactation consultant told me to count from beginning of feed so don’t let LO go three hours from that time before next feed
I've always done it from the end of a feeding because he used to feed for a long time but would go 1hr 15m usually between the end of a feed and the start of the next. Iv just preferred to do it this way but most people do it from the beginning of the last feed x
Beginning
I always do it from the beginning of the feed so say if he feeds at 11 he will then feed at 1-2 but if he’s sleeping he can là until 1-30:2:30 depends on how hungry ur baby is