Query re the event log time stamps vs server time/DateTime.UtcNow

We have a some logging in a community for saml sso requests and the data contains a timestamp acquired with the core DateTime call as below 

so we create a timestamp

var timestamp = DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ss.fffZ")

This is then logged with the Event Log api 

Apis.Get<IEventLog>().Write(...)

But when we view the log entries there is a big difference between the time in the message data and the time of the event log entry, I would have expected the time to be exactly the same bar maybe a second or 2 

In the example below the different is 5 minutes 



Can anyone shed any light on this ?