I just had a very similar question come up, but it was regarding creating filters excluding people who have received an email from us in the last day.
Does 1 day equal 24 hours or does it equal 1 calendar day? After scouring Topliners, running some filters and examining the overlap, and finally contacting Eloqua support, we determined that 1 day equals 1 calendar day. For your case, I would think that 1 month equals 1 month from the time the contact landed in the wait step, so the email should have been sent on April 25, but based on your results it would appear that 1 month equals 30 days.
You would think this would be straightforward, but it's really not, and someone should post a time frame definitions document so that this can be clarified. I'll bet it would be a popular document since timing is everywhere from campaign canvas, to filters, to reports.
