Timer-based Event Triggers

I am currently working on a project with specific requirements. A brief overview of these are as follows:

• Data is retrieved from external webservices
• Data is stored in SQL 2005
• Data is manipulated via a web GUI
• The windows service that communicates with the web services has no coupling with our internal web UI, except via the database.
• Communication with the web services needs to be both time-based, and triggered via user intervention on the web UI.

The current (pre-pre-production) model for web service communication triggering is via a database table that stores trigger requests generated from the manual intervention. I do not really want to have multiple trigger mechanisms, but would like to be able to populate the database table with triggers based upon the time of the call. As I see it there are two ways to accomplish this.

1) Adapt the trigger table to store two extra parameters. One being "Is this time-based or manually added?" and a nullable field to store the timing details (exact format to be determined). If it is a manaully created trigger, mark it as processed when the trigger has been fired, but not if it is a timed trigger.
or
2) Create a second windows service that creates the triggers on-the-fly at timed intervals.

The second option seems like a fudge to me, but the management of option 1 could easily turn into a programming nightmare (how do you know if the last poll of the table returned the event that needs to fire, and how do you then stop it re-triggering on the next poll)

I'd appreciate it if anyone could spare a few minutes to help me decide which route (one of these two, or possibly a third, unlisted one) to take.

Why not use a SQL Job instead of the Windows Service? You can encapsulate all of you db "trigger" code in Stored Procedures. Then your UI and SQL Job can call the same Stored Procedures and create the triggers the same way whether it's manually or at a time interval.