According to this documentation:
Roll snapshots represent the state of rolls for a given block. Roll snapshots are taken every BLOCKS_PER_ROLL_SNAPSHOT = 256 blocks, which is 16 times per cycle. There is a tradeoff between memory consumption and economic efficiency. If roll snapshots are too frequent, they will consume a lot of memory. If they are too rare, strategic participants could purchase many tokens in anticipation of a snapshot and resell them right after.
But this does not say on which levels the snapshots are taken. It's likely that the answer is either
0, 256, ..., 3840 or
256, 512, ..., 4096 but it's not specified which one it is.