The following sequence of actions are needed to add an "all day" event in Google Calendar.
Format Date Time
Configuration
In the "string value" field, using the token picker, add the start date from a previous action in your workflow or enter it manually
In the format field enter MM/dd/yy
Add Date/Time
Configuration
In the "base date" field add the "convert end result" from the token picker
In the "days" field enter 1 (or for multiple day enter the number of days the end date falls on)
In the String Format Field enter MM/dd/yy
Create Event (Google Calendar action)
Configuration
Add your connection
Under "calendar" choose the calendar to add the event to
Customize the "event information" to your liking
Under Event Schedule add the "convert start" in the "start time" field and "add date/time" result in the "end time" field
It is important that you change the timezone from "auto" to your local timezone
This should produce an event that looks like the following graphic in the calendar
