Adam, a turnback on the first leg of a 600Nm trip causing us to refuel again as quick as possible, as not to compromise the arrival time before SS many hours later. The other one was a few days later on the return trip as the result of accumulated small delays and slower groundspeeds as planned, in face of airport closing time, hours before SS.
BTW, interesting was: I had to refile the first leg, so my initial question to ATC over the radio was, could they refile it with adjusted times. After some minutes it was answered the FLPL data were delivered "by another system" (SD thus), and they could not modify that. So then we tried the in flight option, which worked!
Only the LOG was compromised, as the original SD NAV plan was not only interrupted, but that we diverted to another APT, in this case the departure APT.
GrahamB: this is what our (Dutch) AIP says, in both cases a FlPl was mandatory due to leaving/arriving to the country. Some countries have made bilateral agreements with specified neighbouring countries, alas ours hasn't.
184.108.40.206 Time of submission
← (ICAO) flight plans shall be submitted at least 60 minutes prior to departure,