Calculating Time based off regular text fields

Hello,

I am using text fields for time. My reason for this is because iPads tends to glitch out with PDF date/time formatted fields. iPads make it difficult to select a date/time because the pop-up field moves around/doesn't go away, even after selecting from the pop-up menu.

I would like to have a custom calculation that calculates the total time between "Arrive Job and "Leave Job".

As you can see in the screenshot below --

an example would be:

Arrive Job: 8 Hour 15 minutes AM

Leave Job: 1 Hour 15 minutes PM

I know that this equals 5 hours.

So i think the logic would be:

Arrive Job Hour + Arrive Job Minutes

(Leave Job Hour + Leave Job Minutes)  - would think that this should convert to military time if possible : so that If value = PM, and then if value = 12,1,2,3,4,5,6,7,8,9,10,11 - then subtract Arrive Job Total from Leave Job Total so 13 - 8 = 5.

If the example was:

Arrive Job: 8 Hours 15 minutes AM

Leave Job: 9 Hours 15 minutes AM

I know this equals 1 hours

So i think the logic would be:

Leave Job Total (subtract) Arrive Job Total = 1

Please let me know if this is possible -- or if there is another way to capture this data in an easier - please let me know.

I'm doing it in this way instead of having 1 field because I think that users would enter in their data in a variety of ways (8:00, 8, 800, 8;00, 8,00)

The users are construction workers and the process needs to be extremely easy and fool-proof.