Email opening times

I send a lot of Business to Business emails. Normally there aren't many trends, but recently after looking at the opened over time statistics I've spotted that the further away you get from the date of the initial email being sent, the more people open their emails at about 11 am.

I've no evidence as to why this should happen. Maybe it's because there's a slow down before lunch and people are more likely to take a glance at an email they thought they'd save for later.