Install OnTimer is the method that can be used to do this.
Install OnTimer Script is a script step you can include in a script to start your "timer". You then create a second script that uses show custom dialog to open your dialog for collecting the number and set the Install OnTimer Script step to perform this script.
You then use a third script with Install OnTimer Script but no parameters specified to halt the timer when you are done.
WOW! this is exciting news....thank you PhilModJunk.
Would you mind walking me through the steps?
Create script named "Record Data"
SHow Custom Dialog ["Please enter a value" ] ---> specify a global for recording the data.
If [Get (LastMessageChoice) = 1 //OK was clicked ]
Set Field [YourTable::YourDataField ; YourTable::GlobalFIeld]
Set Field [YOurTable::GLobalField ; ""]
Create a second script to perform the first every 20 seconds:
Install ONTimer Script ["Record Data" ; interval: 20 ]
Create a third script with just this step:
Install ONTimer Script 
and perform it to halt the timer.