It is only one hour earlier than the shift my previous company had.

[tufguy]

John is telling Toby about his job timings.

1) My current job shift starts at 6 AM. It is only one hour earlier than the shift my previous company had.

2) My current job shift starts at 6 AM. It is only one hour earlier than the shift my previous (company's) shift.

3) My current job shift starts at 6 AM. It is only one hour later than the shift my previous company had.

 

[GoesStation]

If he were American, John would say something like I start work at 6 AM. That's an hour earlier than I started at my last job. There's no need for "shift" if you're talking about your job unless your schedule changes regularly: I work different shifts. Right now I'm starting at 8 AM, but next week I switch to the graveyard shift. I'll be starting at midnight.