St Pancras station

Yes and no. When you leave the train, you pass through a passport hall and customs zone to reach the concourse. Normally, there are no checks when arriving from Paris (since these are performed in Paris before departure) but I have once or twice over the years encountered random checks. These seem to be trivial, but I have a British passport anyway (I imagine they're checking no one has somehow stowed away, as any immigration questions have already been asked in Paris).

so would you say that it takes 10 min to exit out the station to be on the public road assuming that they are not checking? thank you for the info

No passport check, 10 minutes from the train stopping to getting out into the street (or to the underground). Most of that will be queueing up to get out of the carriage.
Both French (exit) and UK (entry) passport checks are made at Gare du Nord before you get on the train, which is why you have to be at the station at least 30 minutes (45 recommended) before departure.
As you come down the moving walkway from the platform, there are customs people hovering, but they only pull over a few people from each train; try and not look suspicious.

Make sure you allow enough time to get across London to your tour destination.

thanks all. I am trying to reach King's Cross Station, Pancras Road, Bus Stop T for my tour meeting time. I was told that it only takes around 10 min to walk from st Pancras station to the meeting point. Is that correct? Thank you everyone.

That would be 10 minutes from the station once you've got off the train and exited the station. Not 10 minutes from arrival at St. Pancras.

It wouldn't take much time at all for me - but I'd not be carrying luggage. It seems a strange, pretty much quite strange place to pick up a guided tour.....

Once you pass through the frosted glass doors you can turn either left or right. Where you want to go is basically pretty much directly behind you, through the impenetrable brick wall. Turn right and right again through the Eurostar departures queueing area to the exit door and walk down the pavement to what I think is the first bus stop on that road. Or turn left and when you get close to the Underground turn left and go out the exit and turn left and the first bus stop you see should be "T".

Either way is about the same time, I'd probably guess 5 minutes or less from the frosted glass doors, but I know my way and can dance around any queues or milling groups.

It all depends on where you are in the train and how much blocking action there is from passengers ahead of you in the rat-maze before you get down to the frosted glass doors. Could be 10, could be 25 minutes. Nobody really knows. Passing can be difficult if they spread out because the corridors aren't really very wide (the walls are actually one-way glass and everybody is unobtrusively observed).

St Pancras is across the road from Kings Cross Station. Use google maps satellite view to see how close they are. 5 minute walk at most but because you never know what might happen allow yourself 10-25 minutes to gather your luggage, Exit the the train, walk outside St Pancras, stop at the light then cross the road and into Kings Cross station.

Very easy transition to make!