Colchester Council planning committee granted the club permission at a meeting attended by about 250 people on Thursday.
The club had argued the extra hours are needed in order to gain category two Premier League youth academy status, which would put the club on a par with some of the top clubs in England.
But Terry Shuttleworth, a spokesman for the campaigners, said: “The club offered no convincing argument as to why their Grange Road facility should be open seven days a week between August and April other than the fact that by seeking Premier League academy status without having the required facilities, they have bitten off more than they can chew.”
He added: “It seems that in modern Britain everyone must bow down to the Great God Football.
“Why else would a group of councillors elected to serve and protect the interests of ordinary hard-working families simply cave in to the demands of Robbie Cowling?"
Approval means the Grange Road training ground can be used between 9.30am and 3.30pm on weekdays between August and April and between 10am and 5pm on weekdays in July, but the residents claimed a small victory, with councillors agreeing no tournaments, youth or otherwise, can take place between May and June.
The application was approved by seven votes to four.
Mr Shuttleworth added: “Once again, a very small football club, of an average gate of 3,500, gets a very big leg-up from Colchester Council.
Theresa Higgins, chair of the planning committee, said: “We are a quasi judicial committee and we have to follow the laws of the land.
“When a planning application comes before us, in order to refuse it, we have to have material planning considerations.
“During the debate, nobody offered a motion for refusal. The only proposal was one for acceptance with conditions.”