First, the easy question. You can have multiple timers trigger at the same time. Mind you, if you have 100 timers set at the same time, it will take a while to trigger them all if you have them setup individually ( a group would trigger them all at the same time).
As for how timers are processed, we just ensure proper transmission via the PLM. Have you tried, when the device is connected to the outlet, to use the main area screen to turn the device on / off outside of the timers?
Also, have you tried setting up a second / third timer for the same device at the same time for a retry? It sounds like there may be a noise issue on the outlet – any big appliances nearby?
We considered checking the status, but you get into some complexity, such as what if the user turns off a light within the same minute a timer turned it on? Then we would need to monitor user action during a timer event – it gets a little tricky from a user perspective on how that would work – logically.