Someone pointed out on a local email list that the ending time for Tish'ah BeAv is listed differently - significantly so - at various institutions in our local community. He noted the following times published:
Large Orthodox A and Large Orthodox B 9:20
According to the Orthodox Union, none of the above times is even close (within a minute or two) of the Zemanim I would expect:
Tzeis 42 Minutes 9:14 P Tzeis 72 Minutes 9:44 P
The closest is Chabad, which is posting a time 6 minutes earlier than the earliest time listed at the OU. Furthermore, the differences in times seem to only occur on fast days; this year's 9 Av schedule appears, to me, to have the most widely divergent times published here.
What accounts for this disparity? What formula(e) might these organizations be using that they disagree so markedly?