About 2 hours should be allowed for each of the 10 theory units, but complete beginners with no previous knowledge of general science or biology should allow more.
As for the practical exercises, a precise answer is impossible because they are very varied. In Set 1, the first indoor exercise will probably take half a day. Others require an hour or two to set up followed by brief observations at intervals during the following days or weeks. The later exercises in Set 1, and all exercises in Set 2 involve walks and observation time, maybe just around the garden or park, or sometimes further. The exercises in Set 3 involve visits to two different woodland sites, two different grasslands and one other site. These could involve anything from an hour or two spent observing a small copse or a garden lawn, to a whole day’s outing to an ancient wood or nature reserve.