Heathrow T5 to T3
 

How do I get from T5 to T3 in Heathrow Airport and how much tme do I need to do so?

Welcome to Fodors. Assuming this is all on one booking, just follow the signs to "Flight Connections" -- They send you an a bus airside. Generally one will want about 90 minutes minimum for the connection - LHR security can be a zoo sometimes.

Re: my earlier post about travel between terminals in LHR. I'm traveling from Spain (thru London LHR) and onto the USA. May I expect time delays through customs and immigration?

Is this all on one ticket? If so there will be no customs or immigration. Your bags wil be checked through and you just have security.

If on separate bookings its a whole different matter.