I would basically make it this way:
Set two aliases:
Alias One:
- opening a dialogue
- starting a timer
Alias Two:
- check the values in the input form(s)
- check if edited; if yes, do nothing
- if nothing chosen/entered, use default values
- close the dialogue
So you add the alias two in the timer and here you are
I've written many dialogues so far, so please use the help file, the documentation really will include all you need