Hello,
When you click Show SQL in report writer, datetime pick Time frame and recalculate interval of datetime.
You can see recalculation after you click "Execute SQL query" in Report writer. Every click datetime is recalculated.
Datetime can be converted to float and vice versa. If you use report writer template you can pick timeframe and report writer convert it himself.
Floating number representation of a DateTime in SQL server is a number of days since the start of the epoch (since 01-01-1900) in the integer part and the fraction part is the part of the day elapsed since midnight.
Thanks