Do you tell your employer about planned(/ planning) of part time studies in interviews?

As long its taken outside normal working hours, i see no harm mentioning if it is directly related to your field of work, they might even consider subsidizing it!

I will mention my part-time studies to my interviewees, regardless of whether the part-time studies I'm enrolled in is directly relevant to the job position or not. I think undertaking part-time studies demonstrates drive and ambition and initiative, so it can't hurt you. anyway, what you do with your spare time after work is your own prerogative as long as we don't let our outside commitments interfere with our work producitivity.

moreover, the idea of a polymath (specialised in one area but knows enough about many other areas) is trending. watch this fascinating series by CNA, Work is a 4-Letter Word ( https://www.channelnewsasia.com/news/video-on-d... ). so, your part-time studies might just have a direct/indirect impact on the value you bring to your job since it broadens your perspectives.

several junctures in which you can bring this up naturally: one interviewer asked me before, "what makes you tick? tell me about you." other interviewers have asked me about the much-dreaded "how do you see yourself in 5 years' time?"

definitely ask whether study leave or subsidies can be granted towards such pursuits!