2 x 24hr time entry fields calc to X.5 or .0 only

Hey guys, im quite fresh off the boat when it comes to managing pdf files and java script. With that said i do know a little bit, and i have a decent understanding of protocols and such withing computers. 

But im looking for help from this seemingly very friendly community.  I have browsed a lot of solutions, but I cant find one to make this work for me, Im hoping one of you kind folks will help a guy out with a script or 2. 

Heres the rub...

I have a Daily timesheet I'm trying to upgrade so us wrench monkeys can submit time cards that are in fact legible... XD

-Each Job line of the sheet has Start time, Stop time, and Hours total ("Start Time.0" , "Stop Time0", "Hours.0" specifically, field ranges of ____.0 to ____.13 see attached image). Example: Start - 0600, Stop - 1030, Hours - 4.5 // or // 0930 to 1430 = 5.0.

*And yes... i forgot to run the decimal on the Stop Time field name*

-Company policy and procedures dicate that it must be filled using 24hr time. Personally I prefer NOT using colons, so I'd be quite fine leaving them out entirely.  

-Each page/sheet has a Cumulative time worked field ( "Total Hours Worked" )

-Time entries will only EVER be XX.0 or XX.5, no .25's or .4's oir any other odd ducks. Daily max hours is never more than 24.

-This PDF needs to work on IPhone, Android and Desktop apps. 

-We have night shift folks who work 1800 to 0600, and day shift 0600-1800 that all use the same sheet

1) im having troubles selecting a format within the time field options that will allow both 0600 and 1600, the 0 gets removed, or it errors out. I've tried HH:MM, HHMM, HH:\MM, HM, HHM, HHm, Hmm, HMM.

2) How can i get java to recognize 30 mins as 0.5h? Do i need to leave it 

3) Night shift... if i format the fields to a number based calc, then how can i make it recognize that 1800 is less than 0600?

4) Cumulative time fields calc ( "- or ignore" 0.5 lunch). We have to enter our Lunch break as a dedicated and chronologically correct job line (ALWAYS 0.5hr), and I have 2x mutually exclusive radio buttons to indicate if lunch break was taken, by default i have yes marked on sheet. So when I get a script to compile the hour fields into the total field, what script can I use to have it check the value ( " Lunch " -Yes/no ), and then either subract or add the 0.5hr implied value to  "Total Hours worked" field?

5) Lastly (I hope), I am trying to find a way of preventing this file from saving over itself and having to delete all the fields and resave. Is there a way to lock this form from being overwritten? or perhaps only allowing "Save As" function?

5A) is there a way of using the data from the " Date " field to auto-populate the file name? or reference the filename from previously saved timesheets? IE: auto populate a Save as name - John Doe Timecard - dd mmm yyyy ?

Thank you very much for your time and assistance!

Cheers,

Kevin