Guys,
Referring to the CAP371 doc link posted here, please look at section B para 18.2..............and I quote
In a Flying Duty Period involving 2 or
more sectors up to a maximum of 2 hours discretion may be exercised prior to the
first and subsequent sectors.
Your ops manual may or may not include this quote but lets start with the assumption that it does.......
It seems pretty clear to me.....it does not matter why you depart, whether technical, weather or a tight schedule.....you may depart knowing you will go into discretion. You may even start a 4 sector day knowing you will go into discretion.
If you think the schedule is too tight then this will be reflected in multiple discretion reports which the CAA will scrutinize during annual audit.