I have to admit, I can't find any reference to 256MB either. Also, the machines I found on the Time site quoted the 9200 (not 9200se), but in either case, 128MB was the maximum quoted.
All I can think of is, one of three possibilities. Either Time have had these boards produced for their exclusive use, or it is a miss-print, or ATI haven't updated their web site to the latest specs. Perhaps a telephone call or e-mail to confirm would be in order!