It might make sense to post an example that reflects your latest setup - ie lunch column etc... your last file does not have that info. so hard to comment.
Generally speaking using your last file:
E4: =MAX(0,MOD(D4-C4,1)-"7:30")
applied to other columns.
Given roundings and precision involved when dealing with time it's generally a good idea (IMO) to use either Time Strings and coerce (as above) or use TIME function, eg:
E4: =MAX(0,MOD(D4-C4,1)-TIME(7,30,0))
or do the decimal division in the calculation
E4: =MAX(0,MOD(D4-C4,1)-7.5/24)
generally more auditable - ie when come back you're not left with an obscure decimal
In general terms as already outline Time is Decimal - ie noon = 0.5, 6 am = 0.25, 6pm = 0.75 etc... so 7.5 is 7 1/2 days as far as XL is concerned - hence the division by 24 to convert to Hours.

Originally Posted by
FMGSCG
when I type '3' it enters it as '0.03' and throws off my calculations
Check your options - sounds as though you have the "Automatically Insert a Decimal Point" active (to 2 decimals)
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