It is important to understand Excel stores dates and times.
Basically, it stores them as numbers, specifically, the number of days since 1/0/1900. And time is just the fraction of a day. The date/time is just a special formatting on this number.
So, 8:30 AM is really 8.5/24, which is equal to 0.3542 (which is why you are seeing that).
If you want to convert it to a number like "830", you can use the following formula (for a cell on cell A1):