Thanks, Talk merit. Yes,something like what you mention must be going on in the case I was puzzled by.
I was surprised to see that. I thought that the cron job for activity calculation ran every 14 days, but it seems that it may run at hourly intervals for new members. If this is true, then it shows an interesting level of sophistication in the forum ranking system. Obviously new members will be encouraged to post more if they see their activity increasing as they start. Having to wait 14 days doesn't provide the same incentive.