As Ilford doesn't seem to be supplying any data ... a repost of some testing done at Darkrooom Automation:
Tests at exposure times of 2, 64 and 256 seconds showing no noticeable change in density or contrast:
Application note on intermittency and reciprocity:
Anecdotal reports of reciprocity and intermittency effects are likely due to poor timing, failure to compensate for enlarger bulb warm-up/cool-down times and an inability to precisely measure and control exposure intensity.
Application note on measuring and compensating the warm-up/cool-down time of an enlarger bulb: