You can conduct a pilot study in one day as a tabletop exercise if you want. The key is longer, more indepth, and interviewing/evaluating self, artifacts, and participants improve the process.

If you only have one chance to do the actual study, then there may indeed not be enough time to do a pilot study. In that case, you need to be as certain as you can be that you can implement your intervention as planned -- which is what a pilot study would address.

The timeline suggested - a month in advance - seems advisory, and may not be necessary. As long as you have time to recruit participants and schedule the pilot, you can conduct a pilot any time before beginning the study. (If your supervisor agrees.)

A pilot is conducted in advance in order to ensure the data collection process and interaction with the sample population will A) run smoothly without confusing the participants and B) that your study design will lead to the type of responses you hoped to generate (aligned with your research questions).

For example, with regard to interviews you would ask a small group of pilot test participants a few extra questions at the end to see what they think:

a) whether the instructions were clear;

b) whether the questions were clear and wording unambiguous;

c) whether the interview was a reasonable length;

d) should there be an additional questions or were any irrelevant; and

e) do they have any other suggestions for improvement in the process.

You would discuss the feedback with your supervisor and implement any changes to your study design that might improve your outcomes. Roberts (2010) provided a list of potential questions for pilot participants (p. 156).

Roberts, C. (2010). The dissertation journey: A practical and comprehensive guide to planning, writing, and defending your dissertation (2nd ed.). Thousand Oaks, CA: Sage