I'm not 100% sure what you're after, but I'll take a stab at this.
Tableau is grouping by the Lat/Long Combo, which places the Dot on the map. Couldn't you right click on the time field, select the minute format from of your time field, and then you could pull the time field onto size.
Would that work?
In a word, no. With that i'd show per coordinate the minute of a specific time, is not a measure of how much time was spent in the area. That's why I have to work with datediffs.
Thanks a lot!