Ses what the mw has asked you to do is pointless and can only serve to worry you more and rely more heavily on her advice, which is not a good thing. She's effectively asking you to not trust your instincts as a mother.
All babies lose weight after their birth this weight loss is often greater in babies who weigh more.
As long as he is feeding well, the length of time will shorten as he gets the hang of it, ime about 2-3 weeks, and his producing wet nappies and Korma-coloured poo then he's fine.
Do try not to get worried about the length or frequency of feeding, sometimes they take a while sometimes both sides, then the next feed is different. As long as he is feeding as he desires in the early days/weeks then he'll be fine.
Lastly, on what I hope isn't a totally bossy post (sincere apologies) it's maybe a bit early to express. Would you be okay to wait until 3-4 weeks, ideally after the 6 week spurt as you mill supply will have naturally increased.