What are the video timing specs for the GB & GBC ?

Both the GB & the GBC have the same video timing specs. For more info on the various video modes refer to a reference for register STAT ($ff41). Horizontal lines which contain sprites have less H-Blank time available than lines with no sprites. No H-Blank time is available during an active HDMA:

Complete horizontal line timing = 108.7 µsec
V-Blank = 1.09 msec
Mode 2 = 19.31 µsec (~20 machine cycles)
Mode 3 = Variable between 41.37 µsec - 70.69 µsec
Mode 0 = H-Blank = 108.7 µsec - 19.31 - Mode 11

Mode 0 minimum = 18.72 µsec (10 sprites on a line)
Mode 0 maximum = 48.64 µsec (no sprites on a line)