13 hours from Washington to Doha. Then 3 hours in Doha. Then 3 hours to Delhi. Total (According to Qatar Airways)- 18 hours and 45 minutes travel time with transit.
Note- Qatar Airways check in in Washington closes 1:20 minutes before the flight.
8hr 15min to 8hr 30min LHR to DEL by a nonstop flight operated by Air India, Jet Airways or British Airways.
8hr 45min Delhi (DEL) to Brussels (BRU) by a nonstop flight operated by Jet Airways.
The flight duration from New Delhi, India to Thailand, Bangkok is 3 hours & 37 minutes.
The average flight duration from Delhi to Mumbai flight is approximately 2 hours.
3hr 25min to 3hr 40min Delhi (DEL) to Muscat (MCT) by a nonstop flight operated by Air India or Oman Airways.
9hr 10min to 9hr 40min Delhi (DEL) to London Heathrow (LHR) by a nonstop flight operated by British Airways, Jet Airways or Virgin Atlantic.
5hr 25min Delhi (DEL) to Kuala Lumpur (KUL) by a nonstop flight operated by Malaysia Airlines.
2hr 55min to 3hr 10min Dubai (DXB) to Delhi (DEL) by a nonstop flight operated by Air India, Emirates Airlines or Jet Airways.
The flight from New Delhi, India (DEL) to Colombo, Sri Lanka (CMB) takes about 3h 35m duration.
A random search for flights from Brisbane (BNE) to Delhi (DEL) shows: OPTION 1: 17hr 10min via Singapore (SIN) BNE - SIN Jet Airways Flt 4051 Dep 01:40pm 19Feb,Fri Operated by Qantas Airways SIN - DEL Jet Airways Flt 17 Dep 11:10pm 19Feb,Fri Flight Duration: 13hr 30min; Layover Time: 3hr 40min; Total Trip Time: 17hr 10min
08hr 40min by a nonstop flight operated by Air India AI Flt 127
6hr 10min Delhi (DEL) to Shanghai Pu Dong (PVG) by a nonstop flight operated by Air India.