Mimzy never had alfalfa hay either, simply because they don't sell the large bags of oxbow alfalfa around me, only the oxbow timothy. So I agree that switching to timothy hay is no problem. The rest of what the vet said does sound a little strange, I haven't heard of that diet for a 7wk old. I just went to look up the links that binky bunny posted on here in the diet section.
You should find this quite helpful: http://www.rabbit.org/faq/sections/...tml#babies
It says they shouldn't get veggies until they are 12 weeks, and even then, it's just introducing the veggies & I believe this is because any younger than 12 weeks, there is a possibility of upsetting their tummies.
I didn't agree with the diet my vet recommended either, he wants Mimzy on a fiesta diet that has seeds & other fun stuff in it & then to give her a vitamin block. Oxbow has vitamins though & she will only eat the junk in the food and leave the healthy stuff haha.