ScotRail are a 36hr four day week (Sundays outside), maximum turn length 10hrs, minimum turn length 7hrs 30. Three weekly rest day cycle:
Week 1 Fri Sat
Week 2 Mon Tue
Week 3 Wed Thu
Spare turns are based on average turn length, so generally around 9hrs. No "booked spare" turns (except on Sundays) any more, so they all have a 3hr swing if you pick up a job on them. That's to say that if you're 1500 spare, you can pick up any job that starts between 1200 and 1800 on the weekly or daily sheets.
Regards the start and finish times, those are entirely dependent on depot. Its a 24hr job, so you can in theory start any time, like 0100 etc.
Generally speaking, most depots earliest starts will be between 0300 and 0400, and latest finishes 0100 to 0200. Some depots also have nightshift "shed" turns.
Jobs starting before 0500 must be less than 9hrs in length, and nightshift "shed" drivers cannot be used to drive main line trains in the morning.
The longest turns are normally the ones that aren't extremes - so jobs that start between 0600 and 1400 tend to be longest, whereas those that start at 0400 or 1600 tend to be shorter. Mainly, anyway.
This is just an example of one TOC, they all have their own terms and conditions.