With the telegraf gnmi input plugin, in order to use the telegraf timestamps instead of using the devices timestamps:
Here's the fork https://github.com/rski/telegraf that was used for:
influxdata/telegraf#8411
influxdata/telegraf#8420
Until this option will become natively part of Telegraf (influxdata/telegraf#8689), you can build a docker image from this fork:
git clone https://github.com/rski/telegraf
cd telegraf