URGENT: Workflow issue

Hi,

Please help me correct what I'm missing in below scenario.

Note:  XYZ is a picklist field with values as 1, 2 & 3

          A, B & C are date fields

          A is a date field on Object1

          B & C are date fields on other Object2

Objective: If XYZ = NULL or 1 and if C is getting updated from NULL to NOT NULL, then B should get updated on basis of A & notification should go post 5 min of this change. But need to make sure that nothing ahead should trigger this workflow as otherwise duplicate notifications will trigger.

Actions:

1. Wait - 0 min

2. B = A+30 (Using JoinFieldValue function as A is on different object i.e. Object1)