Trigger WC in Approval Workflow

Using V7.1. I have some approval workflows that include some Wait Conditions that call a SQL Function to determine if the approval workflow should move to the next step. It's working fine, just that while I'm testing sometimes the step goes through almost instantly but sometimes I have to wait upwards of 15 minutes - in these circumstances I have gone into SQL Server Management Studio and run the function and I can see it returning a positive value - so if the WC had been evaluated, it would have passed that step straight away.

Is there anyway I can trigger the Wait Condition to evaluate? I looked in DialogSchedule and couldn't see anything that looks related.