I pass on that side of the station every morning, but to be honest I'm always later than late, so I wouldn't stop during the week. However the Westbourne Cafe in the corner is always packed so there are people with time in their hands in the area.
I would definitely use a patissery/bakery at the weekend as long as it had a wide selection of cakes/pastries (something like Patisserie Valerie in Bromley) and proper coffee (like Cafe Italia in Soho), but that maybe would be too upmarket for Forest Hill?