Earliest Time in my data

Morning, 

I hope someone can help me.

In the _m_overallstarttime column I want to repeat 07:09 time for each row.

07:09 represents the first issue of the day and I need that in every row where there is a reference number, so a variance calculation can be shown. I am only looking at a daily view so have a calendar date slicer in my report which cant be ignored as depending on which date you select the first issue will be at a different time, anywhere between 05:00 - 23:59.