I’m an agency driver that works in an office Monday-Friday, and drives HGVs on weekends, (at most) one day per fortnight.
I’ve been doing this record-keeping ever since I restarted HGV driving last year - doing manual entries for every day spent in the office - at least, a reasonable approximation of my office hours. I don’t record it as to-the-minute accurate, but just record 9am-5:30pm with an hour for lunch. In reality, my hours will be slightly different to that, but my actual hours are always well within the requirements of the regs that the deviations are irrelevant.
I’ll typically spend a minimum of 20 minutes at the start of a shift (sometimes as much as 40 minutes) doing manual entries, because it takes so long just pressing the buttons, and I’m careful to make sure that everything is correct so that I don’t get an infringement. Working for a large supermarket chain, they’re pretty hot on telling us that we have to be absolutely perfect on manual entries, so they’ve never complained about the amount of time it takes.
Note that if I have a 3-week gap between shifts, it’s actually impossible for me to do a proper set of manual entries. This is because the tachograph head has a limit on the number of manual entries that can be made per card insertion. Each working day has four mode changes (morning work period, lunch break, afternoon work period, overnight rest). Three weeks, five working days per week means sixty separate entries, and the tacho head simply will not allow this many manual entries. In theory I could miss out the lunch break to reduce the number of mode changes, but then I’d be recording myself has having broken WTD requirements for mid-shift breaks.
This might just be a limitation of the tacho heads that our trucks have, but I suspect that it might have been part of the EU specification - the digital tacho cards are designed to have enough storage for a specific number of mode changes before it starts overwriting previous data; if they allowed an unlimited number of manual entries, then it might be possible to put in a huge number of manual entries in order to “lose” the record of a previous infringement.
I’m reasonably sure that the regs used to be that you only required records for weeks where you drove under EU regs. If you didn’t drive under EU regs for the whole week, you weren’t required to have a record. However, I’m currently unable to find evidence to back this up, so maybe this has changed (or it was never true in the first place).