The Immigration office is about 200 m from the Bhutan Gate. Its timings are 9am to 5pm with a one hour lunch break. There is quite a queue on Mondays, so be there by 8:30am.Documents needed for Indian tourists:1. Passport/ Election ID for Indians (original and xerox)2. Passport size photographs3. Hotel reservation copies for the rest of the trip4. An Itinerary or travel plan copyOnce done submitting these documents, they take about 30 min to validate them and then call for biometrics. Overall the process takes about an hour.There is a xerox/ print out/ SIM shop exactly opposite to the Immigration office. We bought a SIM for the rest of our trip once we were issued the permit.