More information on Cosmonautics day is available at http://en.wikipedia.org/wiki/Cosmonautics_Day.
**UPDATE** April 7
ARISS Russia coordinator has stated that the event will operate on April 12 as well during the same 10:00-21:30 UTC time frame.
**UPDATE** April 9
The Russian crew plan for the weekend has been updated and if I am reading it properly, SSTV will setup starting at 10:00 UTC on April 11 with control checks at 21:30 on April 11 and 08:45 UTC on April 12 then shutdown at 21:30 UTC on April 12. That will provide about 35 hours of continuous operation.