If catching this bus in Rangsit, where exactly do I board ?

How far south on either Wiphawidi - Rangsit or Phahonyothin Roads (and which of those)? does the bus go before turning east ?

And, approximate travel time to the airport ?

you can also take the nr 555-an orange BMTA-the 554 is shiny yellow private, both end at BUSterminal Swampy-in the far end,

I guess you have ever taken a bus before; so you should have noted that buses stop at busstops-ALL those designated along their route-where usually dozens till a few 100 Thai are waiting along the road and some shelter with ads for the BMA are. BOTH lines go south along Viphavadee, pass old Don Muang, then at Laksi crossing the 554 truns left into ChWattana-Ram Indira and follows this till the KM 8-then south along Bangkapi. The 555 runs further south-along Central, besides the expressway, left along Din daeng, goes up on expressway before the Fortjune. As you may know, BKk may suffer from heavy traffic at times, so times are all unpredictable-reckon on at LEAST 90 mins-and likely more in peaks or when jams hit.

These routes start at the official garage-for the555-where noone will know and you too-then simply follow like any R'sit bus along the main road-market and the main stop in in front of the Major cinemaplex-where there are also hordes+droves more of minivans-incl. also for 554/555.

Try in front of major cineplex, Future park Rangsit