If I understand your scenario correctly, you actually have 3 objects: 2 bar charts and 1 straight table. (If that is not correct, my apologies). Assuming your straight table has at least one column that is a field in your data model, for example "start_time", then you can specify one of the following in the bar chart's Layout->Show->Conditional expression:
GetSelectedCount(start_time)=1 bar chart appears when one and only one start_time is selected in your straight table.
GetSelectedCount(start_time)=0 bar chart appears when no start_time is selected in your straight table.
GetSelectedCount(start_time)>1 bar chart appears when any start_time is selected in your straight table.
If you're looking for the selection of a specific value, then use: start_time='the value' in the expression.