Offset the timestamp before saving data

I have devices sending JSON format messages using MQTT. As battery powered devices they store multiple measurements until they reach out and send all measurements adding the age of each measurement in seconds (“o”: seconds).
Two typically message would be:


which messages are 60 and 120 seconds old.

I want to adjust the timestamp before storing the data in influxdb. What would be a solution?
One option I see is to use Golang and apply the time.add function. Any examples or directions to look for?

What kind of adjustment do you want to do, what is the goal?

I get 10 measurements once each 10 minutes (from each device separately). I want to put each measurement on the timeline it (=the measurement) was created and not when it was received. (all 10 on the same timestamp).
As the device is not aware of the absolute time, I need a processor to help calculate the timestamps based on the offset (540, 480, 420, 360, 300, 240, 180, 120, 60 or zero seconds) provided.
Timestamp = (time.Now()).Add(time.Second * - Field('o'))

Other solution would be a python script listening to MQTT messages, doing the calculation, and resending it to Telegraf. Or having the device spending 2 seconds for a NTP-call lowering the lifetime of the device. So I am searching for a solution within the Telegraf/InfluxDB domain to keep it simple/keep it transparant and easy to maintain. What solutions are available to me, respectively advised?