Over here without any external lights within 500 m (tho' unfortunately there are far more lights showing on the western side of the bog these days as farmyards invest in powerful orange sodium floodlights) and 8/8 cloud cover I couldn't see my feeders minimum 15m away without using bins until 7.57am. First out were blackbirds underneath and then a robin on the feeder at 07.58. Next a great tit at 08.10 by which time it was 'light' and the usual clan arrived in a rush between 08.15 and 9.00. I would be surprised if birds didn't feed earlier in well lit locations but there are lots of variables in these surveys: how many feeders, what food, availability of natural food, how close to the observer, how good observer eyesight, weather, presence of predators such as cats and owls which can see in the dark probably better than tits…
Worth having a go as you never know what you might see!