Either is fine with me.
Logistically, the first is probably the superior of the two, as anyone travelling from outside the Rhein-Main area will find it easier to arrive early and get back in the evening, as opposed to afternoon and then evening, since that may well entail an overnight stay and the ensuing expenses.
Of course, we can actually plan both: an entire day of watch stuff. After Sinn, if people are so inclined, we might visit, for instance, Windecker in Oberursel for a look at his new Manufaktur and then retire to the Oberursel Altbrauhaus for a heaty evening meal and consumption of either alcoholic or non-acoholic beverages. Or alternatively we could hook up with one of the other watchmakers in the area: L'Horologie in Bad Soden, for instance, or
perhaps someone else can come up with an alternative?
If we decide to do Windecker, I'd need some notice ASAP so that I can arrange it with him...