Assuming a community where all who are eligible to say kaddish say it together:
The anniversary of a relative's passing is on the 16th of Av which happens to fall out on Shabbat, which begins at 7:59. If the person goes to the early minyan which begins at 7PM does he say kaddish during kabbalat Shabbat which will be said while it is still the 15th?
Does accepting the status of Shabbat drive his saying kaddish or must he wait until the proper date (the time after which the calendar would reflect the correct number)?
If he does say kaddish, and then hangs around until the regular minyan comes in and says mincha, does he say kaddish after aleinu at that mincha minyan (which is a davening part of the "previous" day)?
Though this is related to this question, it also seems to border on a discussion of what it means to take Shabbos in early, which appears to bring up all sorts of other argued points regarding the status of the individual and the day.