A reader tells us that the block of 6th Street between 4th and 5th avenues in Park Slope will be closed for more than two months, due to construction on an apartment building near the corner of 4th Avenue. (On the same corner, a large Karl Fischer-designed apartment building is also going up.) Residents received a letter in the mail this past weekend from the developer of the smaller of the two projects, known as 278 6th Street LLC, notifying them of plans to shut down the street to traffic from 9 am to 4 pm on weekdays; deliveries and parking for residents will be allowed. However, said our tipster, they are already running over their permitted hours, parking all over the block and in front of fire hydrants, blocking the pedestrian walkway and making pedestrians walk in the street (even after hours) — and street cleaning was skipped Thursday, although the developer promised to accommodate it, along with garbage pickup. Two complaints for after hours work have already been logged with the DOB in recent weeks. “For the past several months, we’ve had to put up with a lot of construction noise, sidewalk closures, massive trucks and cement mixers blocking the street,” he said. “I just talked to the guy who runs a tinsmith business right next door to the site — for most of us it’s just an inconvenience, but he says it’s totally killing his business this week.” Click through for more photos of the block, all taken at 4:10 in the afternoon yesterday, according to our tipster.