When in doubt, I use the Massive DEvelopment Chart: http://www.digitaltruth.com/devchart.php. It indicates a dilution of 1+100 and a time of 15 minutes, with standard agitation. This could be difficult if you have only a single roll in a small (250 ml) tank, since it is recommended that the tank contain a minimum of 5 ml of Rodinal per roll to assure complete development. The easy way around this would be to use 5 ml in a 500 ml tank, and add a second empty reel to keep things from sloshing around too much during agitation.
Hope this helps!