Adjustment Dock Expose Activation Time
I'm not knowledgeable about a setup for simply clicking the symbol with the computer mouse apart from a default for transforming it off ...
defaults write com.apple.dock show - expose - food selections - boolean
You can transform the practices of when you drag a documents onto a dock symbol though ...
Go to Finder Preferences and also at the end of the basic tab there is "Spring - Loaded folders and also windows"
You can dis/enable it and also transform the hold-up time.