Avoid following or intruding into private spaces to interrupt internal/sleeping/feeding routines. Waiting a few moments (you can skip a few hours using 't' to wait even if you are not near an available bed) reduces the frequency of important characters becoming non responsive. (You will also see more of the non-stressed dialogues or routines than if you 'rush' everyone, and will commit fewer crimes).
Avoiding crimes in general reduces the number of interruptions in interactions - entering homes, stealing, running into people (or standing in the circulation routes), not carrying a weapon inside towns (deselect in the inventory at night) or walking in town without a light after dark (select in inventory at night) are all things which feed into the crime system, and can interfere with some activities (including multiple simultaneous arrests and murder for non-response).
If you cannot speak to one of the quest givers prior to finding Pribslavitz, then these quest segments are concluded by that discovery. Only subsequently talking to Robard can be a game breaker, and one of the options for reinforcements (5 iirc) causes a problem too.
It is possible to complete the main quests inside an hour quite comfortably once you know the general flow, and without excessive side activities or exploration two or three hours is sufficient (especially if the herbalist to the NE of the woodcutter is used instead of the one near Samopesh). I tend to do much more than this, as I like to obtain all dialogues as I go to increase speech skill as much as possible and to walk/trot more than run or sprint/gallop everywhere.