Sunset is around 6:36 pm these days and ideal twilight is 6:53 pm So 6:30 pm would be a good time to meet. If you come later, no problem you can catch up to the rest of us.
Parking cost seems to be $9 for three hours.
FYI: On Weekends you can park there for about $5 all Day.
Note there are two garages on Caroline St. one further South i.e. closer to Fells point is more expensive and it not the one described here.
You will come to cheaper one (i.e. listed here) first if you head south on Caroline St.