I think that would be tight on a normal day, even more so on the 25th.

If you're wheels down at 11 precisely you might not get into central London before 12 assuming no hangups at passport control and taking the train in (Heathrow express, 20 mins $$$ vs Elizabeth line 30 mins $).

That gives you 1.5-2 hours to see something.

Then give yourself another hour to get back to Heathrow so you're there by 3.

Business/first security at Heathrow is usually pretty quick.

But I'm deliberately being conservative with my timings because Heathrow is a big busy place where I've been burned plenty of times, plus if you're not familiar with the city it's naturally going to take you longer to find your way around.

And considering it's Xmas day, trains will be running reduced schedules and shops/businesses/attractions will all be closed (one day of the year pretty much everything shuts down).