With the resistor included in my configuration, when you apply power the capacitor is in a discharged state, holding the trigger at (-). The resistor charges the capacitor, pulling the trigger high, allowing the timer to start. When you remove the power the resistor might discharge the capacitor, readying it for the next timer cycle. I would add another like value resistor from +V to -V, to assure this. This all assumes that the timer circuits works that way. But without a schematic, I'm just guessing.
Ken