Look at the box in the lower right corner. I think you need to set a time when the door opens. Try setting the time in seconds, and then a Fraction of 1, meaning fully open. Check the User's Guide to confirm. I have not used this feature in a while.

Here's an example input file with a simple vent closing. For the GUI to work, you'll need to put in more than one input into the vent opening fraction window. I've put three entries in: an initial fully open vent at 0s, the start of the vent closing interval at 1 s which then transitions to fully closed in another second.

An input file saved from this is as follows:

&HEAD VERSION = 7700, TITLE = 'CFAST Simulation' /
 
!! Scenario Configuration 
&TIME SIMULATION = 3600 PRINT = 60 SMOKEVIEW = 15 SPREADSHEET = 15 / 
&INIT PRESSURE = 101325 RELATIVE_HUMIDITY = 50 INTERIOR_TEMPERATURE = 20 EXTERIOR_TEMPERATURE = 20 /
 
!! Compartments 
&COMP ID = 'Comp 1'
 DEPTH = 2.4 HEIGHT = 2.4 WIDTH = 3.6
 ORIGIN = 0, 0, 0 GRID = 50, 50, 50 /
 
!! Wall Vents
&VENT TYPE = 'WALL' ID = 'WallVent_1' COMP_IDS = 'Comp 1' 'OUTSIDE' , BOTTOM = 0 HEIGHT = 2, WIDTH = 1
 CRITERION = 'TIME' T = 0, 1, 2 F = 1, 1, 0 FACE = 'FRONT' OFFSET = 1.3 /
 
&TAIL /

Thank you so much, this worked. Have been trying to get this to work for two weeks!