In that case, the best you can hope for is to centralize time on the server. The IoT devices can keep local differential time or contact the server (or a log se

In that case, the best you can hope for is to centralize time on the server. The IoT devices can keep local differential time or contact the server (or a log server or somewhere else) at the time of the event. It's kind of messy, since you are asking to trust a client's data, which is untrustworthy.