I started off being incredibly meticulous about maintaining time. I'd keep a notebook, round to nearest 5 minute interval and exclude any time spent on breaks, regardless of how inconsequential.
This approach pissed off nearly every Witness I went to service with, especially other regular pioneers. I discovered quickly that nearly everyone of them was knowingly exaggerating their time. With some of them, their justification for counting time the way they did went beyond farce. I've shared some of those stories here over the years.
During my final two or three years with the Witnesses, I would write down a few hours on a time slip every now and then. Sometimes I just hadn't kept good records and guessed. On some occasions I just didn't care and wanted to avoid being labeled as an "irregular" publisher. As someone mentioned above, the elders did not care. They lied about time themselves. The congregation secretary didn't want the hassle from the circuit overseer, so he was more than happy if you "estimated" a few hours every month.