Data Format Changing Back To Automatic

I am trying to create a timesheet calculator and am running into multiple issues.I keep changing a cell's data format to time, but as soon as I type anything, it goes back to automatic.

1) Why does the cell's data format keep changing back to automatic?

2) Is it possible to have a spreadsheet that I can type in hours such as "7:08 pm" as "7.08" and have it convert to time if it's in a cell with a time format?

3) What's the best way to create a time sheet? I need to have a time in and time out -30 mins for lunch and then the total as a decimal.

I have attached a picture of the automatic data format issue and a picture of what exactly I'm trying to do, if anyone has a better solution...