My LO was on roughly on a EBM bottle from 3 weeks, as had to return 1 day a week from 1 month and full time at 4 months.
Also had the advice from the MW to do before 6 weeks if it was something you wanted to do. I know of a LO was had a few bottle before 6 weeks and then none, when they tried to give bottles again at 3 months, she wouldn't take it and they tried everything, so I think it's worth keeping up every other day or so.
I'd recommend looking up how to bottle feed a BF baby, as our culture of trying to get them to take all of it, can lead to problems and overfeeding. The only time we had problems was when she had bottles for 12 hours. I knew it bottle related as she would stop crying the moment the teat touched her mouth. At that point, I stopped giving her bottles and rode it out. A week later, I reintroduced a bottle. I didn't know about how to bottle feed her, and had left her with my mum who had FF. So if you look it up, make sure to brief your carer.
Also explain to them that BF only have about 25oz (after 6 weeks) regardless of age, otherwise they might think your starving her and try to persuade her to take more IYSWIM. Don't stress if she only takes 1-2oz at first and don't compare amounts to FF babies otherwise your scare yourself something silly 
Kellymom, naturally has a good expressing section, including a how much will my baby need calculator and information on storing BF
hth