AVRs can work comfortably at 6.24v.
Sure they can that is why the data sheet says
Maximum Operating Voltage ............................................ 6.0V
and then goes on to say
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent dam- age to the device. This is a stress rating only and functional operation of the device at these or other conditions beyond those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Oh but I forgot according to you data sheets are a conspiracy and only to be used if you are designing equipment for NASA