Mad Flt Scientist, the same is true for the Airbus DFDRs.
25 hours is the minimum that they have to record, with the right combination of capacity and data rate they can actually record 50 hours.
From the manual again.
The DFDR is a solid-state flight-data recorder in compliance with ARINC 717. The DFDR stores all aircraft information in CMOS bulk erasable EEPROM (Flash Memory IC) devices. Being a solid state device, the DFDR has no moving parts. The recorder can store all data which the FDIMU has collected over the last 25 hours. It is possible to store more than 25 hours of data if the correct combination of DFDR capacity and data rate are used.
Data is stored in shock protected solid state nonvolatile memory device (CMOS). The recorder receives 64,128 or 256 words/sec series messages from the Flight Data Interface Unit (FDIU). The write mode is a single channel incremental block recording with inter-record gaps between each data block. One data block contains data received during one second (768 BITS). Throughout this recording phase the DFDR continuously monitors its correct operation. If an abnormality occurs during this time it is automatically memorized (BITE function).The recording duration of the recorder is 50 hours under normal flying conditions. After the aircraft has landed, the memorized data can be transferred for analysis.
The correct answer to the Original poster I guess is
DFDR - 25 hours (rising to 50 hours theoretical)
CVR - 30 mins
SSCVR - 2 hours (although SSCVR are still referred to as just CVR).