I guess the answer depends on how one defines "smoothly", but for me it was about 18 months in. That was when I finally felt full confidence that I could negotiate the ups and downs of life without *fear* that a relapse would leap out at me from behind a bush and take over.
The defining event was a trip I took to Bath England for a concert, and involved all the hassles and stress of 8 times zones as well as many potential triggers including lots of drinking at Bath Pavillion, and whiskey stores or pubs seemingly on every block. I brought my laptop to check in to sobriety support sites, but otherwise I made no specific plans, I wasn't worried about relapsing, and it all turned out fine.
That was the last bit for me, losing the fear. Day to day life had been pretty smooth after 6-10 months, but before that trip I still kept a pocket of fear and dread about new (to sobriety) situations.