Heathrow to Kensington After 9:00 PM

For the cabs regulated by Transport for London, here's a place to start: https://tfl.gov.uk/modes/taxis-and-minicabs/taxi-fares . It seems that the time of day/night doesn't affect fares between Heathrow and Central London, as I read the chart on the page with general fare ranges.

There are private car hire firms as well that provide transportation from the airports into London. A couple that are often recommended are Just Airports and Blackberry Cars. I have no personal experience with either of them, but would consider either of them based on what I've read about them on online forums over a period of years.

A taxi you get from the taxistand is always metered. This is also the most expensive way to do this.
What you can do is pre-book a "mini cab". This is a fixed price service, you agree the fare when you book. Google "mini cab Heathrow". Also lots of posts on this website recommending mini cabs.

The cheapest way, and nearly as quick as a taxi, is to take the tube.
The nearest stations for Kensington Church Street are Notting Hill Gate or High Street Kensington, depending on which end of the street you want to go to. And it will cost you a mere £3.10 off-peak with an Oyster card.
A mini-cab will be at least 10 times that.
A proper taxi from the taxi rank will be even more expensive, £50-£60 +.

15 miles, maybe 45 minutes at that time of night - from T3. More if at other terminals or less. If nothing is on.

I don't take taxis that I have to pay for so no knowledge there; regarding the time - my estimate is if I were driving, taking into no account the queue.

Thank you so much!!!!

The tfl website includes an interactive planner. It will show you routes to your hotel address, schedules at your time of day, fares (worth reading carefully), etc.

Google Maps has a similar service, for sake of comparison.

Thank you!!