Space traffic jam: AMS-02 launch postponed to April 29

The launch date of the Alpha Magnetic Spectrometer AMS-02 (“-02” because it is the successor of first AMS experiment, flown into space in June 1998) has been postponed to April 29 (above, an image of AMS-02 in the bay of the Shuttle Endeavor). 
The delay is not due to the severe weather conditions of the past week, that produced only “very minor” damage, but to a conflict with the docking operations of the Progress M-10M cargo ship, a russian vehicle that will deliver up to 2.5 t of propellant, scientific equipment, food, air, water, etc. to the International Space Station (ISS), scheduled for launch on April 27 from the Baikonur Space Center in Kazakhstan. 
Apparently, the problem comes from the time-sensitive nature of the Progress cargo, a biological experiment which needs to be placed into one of the ISS’ freezers within days of launch..
Although postponing the launch by 10 days is not dramatic per se, the launch date is getting uncomfortably close to the end of the launch window (see here a description of how it is determined).