Spend two hours testing the method
You can test out the method for yourself in a couple of hours by
If you decide to continue, you can treat these two hours as a test round.
If you decide to proceed with a bigger study, all observers should participate in one or two test rounds. They need to understand the technique and to agree on interpretation. It may also be necessary to revise the floor plan.
Spend two days -
If you decide to gather data about one typical day at the library, this will require two to three days of full time work:
To get the most from the TTT results, you should gather other types of data at the same time. If you know the number of vistors (gate count) on the "observation days", you can calculate the average length of stay at the library. If you register the number of (physical) loans and returns, you can compare those data with the traffic. If you register the number of reference queries, you can relate that to data on contact with staff.
Spend two weeks
The work should preferably be shared of two or more persons. A full scale TTT study should cover at least one - and preferably two - full weeks. If you want reliable quantititative data, the counting days should be spread out as much as possible. The ideal sampling plan would be one day a month through one full year. A decent alternative, however, is to
The total traffic will probably vary quite a bit through the year. By counting the number of visits on a regular basis, you get data on these fluctuations. The actual usage pattern - how traffic and activities are distributed between zones - is likely to be more stable.
Comparing the first and the second TTT study will give a good idea of the usage pattern and its stability.