SharePoint doesn't have parsing functions to automatically convert text to times. I'd recommend using a datetime field anyway, as that prevents data entry issues as well as makes the time calculation much simpler. If you must allow users to enter text, a developer could add an event handler or implement an Azure function to parse the string and perform the ...
Using the following forumla:
INT(([Tech Checkout]-[Tech Checkin])*24)&":"&MOD(INT(([Tech Checkout]-[Tech Checkin])*1440),60)
Result: Tech Checkin and Tech Checkout are single line of text fields
Calculated Field Formulas
Calculated Field Formulas with demos
Note: If the answer helps you, don't forget to accept it as the best answer. It will help ...
This is not possible by OOTB. But there are many possible ways to achieve it. Along with the link shared by @ganesh in the comment above, you can try these couple of ways mentioned below:
Using Date & Time field and Calculated Column
Create a Date & Time column and a Calculated column with the formula:
=TEXT([Date column name],"hh:mm AM/PM")