Converting Numerical Values to Time to then calculate duration in decimal format

So I'm re-working an excel spreadsheet and want to set it to where co-workers can enter time as just 1340 (24-hour clock) and have it convert it to 13:40 in the cell. I am then looking to be able to calculate the duration between the two times and have the value calculated to time in decimal. So if between 1500 (15:00) to 1824 (18:24) TASK A is completed, it would be 3.4 hours. The current formula is as follows and the problem is that with the ROUNDUP function, it skews the time to where from 1600-1618 is calculating to a 0.4 whereas it should be a 0.3 (18 minutes...).
=ROUNDUP((((MOD(B63,100)/60+INT(B63/100))/24)-((MOD(A63,100)/60+INT(A63/100))/24)+IF(B63<A63, 1,0))*24,1)

Times should be calculating as such:
1-6 minutes =.1
7-12 minutes =.2
13-18 minutes= .3
19-24 minutes= .4
25-30 minutes= .5
31-36 minutes= .6
37-42 minutes= .7
43-48 minutes= .8
49-54 minutes= .9
55-60 minutes= 1.0

The cell formatting for the times themselves is Codigo Postal. I am hoping to keep this as cell formatting and formulas as I am not familiar with VBA macros, etc. TIA

My 1st question would be - why mess with this? Time is time and excel knows how to run calcs with it.

In case you didnt already know, Time is actually a decimal part of 1 (day), so 06:00 AM is 0.25, 12 noon is 0.5 and 18:00 (or 6 PM) is 0.75

Can you upload a small (clean) sample workbook (not a pic) of what you are working with, and what your expected outcome would look like.

Glad you got where you wanted to be

Try this

A2= Start Time, B2 =ENd time
Formula in C2

=CEILING((B2-A2)*24,0.1)