Upvote:1
When transiting airside at Heathrow, dedicated buses will transport you between the terminals, meaning you will not have to clear immigration.
For this type of transit, you do not need a visa, owing to your valid US visa.
If you did need to clear immigration (to pick up baggage for example, which you won't because you have a single ticket), you would need a visa to do so, because then, a US visa holder also needs to be on a journey to/from the US.
However, since there are airside buses, which means you don't need to clear immigration, your US visa alone means you can do this trip without a UK visa.
As for the timing, you will be OK according to Heathrow's flight connection planner: however even if you miss the connection (such as if your inbound from Delhi is delayed), the airline will take care of you since the trip is on a single ticket.