I like to walk too, but on a daily basis, there and back, hmm. I'd stop at 30 to 35 min walking each way, 50 minutes would be too much for me, but then once you start, you'll get used to it quickly.
Tradeoffs - walking one way, taking the bus back on another - although I think I'd prefer walking home to clear my head.
The bike would be more efficient, but there is that argument about sweating on a hot day, so bike in cold weather for a change in pace and take the bus when the weather is lousy.