Here is the explanation from the Premier League website.
As a mark of respect and remembrance for those who lost their lives as a result of the Hillsborough stadium disaster in April 1989, all Premier League, Football League, Football Conference and FA Cup matches taking place on the weekend of 11-14 April will kick off seven minutes later than originally scheduled.
The match at which the disaster took place, the FA Cup semi-final between Liverpool and Nottingham Forest on 15 April 1989, was ended six minutes after kick-off, at 3.06pm.
In the Premier League, Football League, and Football Conference, matches due to kick off at 3pm on Saturday 12 April will now do so at 3.07pm, with the minute before kick-off (3.06pm-3.07pm) having a period of silence observed at all stadiums.
The first FA Cup semi-final on Saturday 12 April between Wigan Athletic and Arsenal will kick off at 5.07pm with a minute of silence between 5.06pm-5.07pm.
The next day, Sunday 13 April, the FA Cup semi-final between Hull City v Sheffield United will begin at 4.07pm with a minute of silence between 4.06pm-4.07pm.
Fixtures kicking off at other times on Friday 11, Saturday 12, Sunday 13 and Monday 14 April will observe the same etiquette with matches starting seven minutes later than originally scheduled.