Does the Sub Job have any different fields/ information from a Job? If it is 100% the same then I would relate the Jobs Table to the Jobs Table and make sure that the reference field is Related Customer Job or something that makes it very clear a given Job is the Sub because it has a Parent.
If a Sub is different in any way, make a new table.
I have a business case for a client where we have to take time cards from employees in the field and then break them into pieces for Payroll. The big distinction is Regular and Overtime for components of a single time card. Just like your case there are different Start and Stops but there is also Related Payroll Allocation Type which a Time Card does not have.