Conversion time-frame at Smashwords has been very long lately, due to a large volume of ebooks being converted.
Considering it took 24 hours for KDP to publish my ebooks in mobi format only, having Smashwords convert my
latest ebook in less than 12 hours and in more formats isn't too bad.
Once in a while it takes a long time for Premium level distribution to be approved, but the conversion time isn't all that bad. My last ebook, published last month, was approved for Premium in about 2 weeks I believe.
I always check the various formats once an ebook is finished converting, and if I see any problems I simply unpublish the ebook, fix the problem and upload the latest version.
Smashwords isn't perfect, as some members of the
Smashwords Forum will tell you, but it isn't the worst thing since the Edsel.