I do all FMQ on my little Singer Featherweight. It takes me anywhere from 8 hours to 40+ hours to FMQ a lap quilt, depending on how intricately I design the quilting. 8 hours would be SID/diagonal straight lines about 4 to 5" apart. 40+ hours would be if I do a pattern specific FMQ with a large number of stops and starts and thread color changes.
I've been quilting about 30 years off and on. Recently I decided to just answer 40 hours for piecing and 40 hours for quilting a lap quilt - not counting the time to find, buy and starch, and cut the material into the pattern - for my "Stock" answer to anyone who wants to know how long it takes. I usually follow up with a discussion about the freedom to choose what you do and how you do it.
This answer helps me feel better when I look into my closet, see all those UFO's sitting there, and can't figure out why things are not getting done! I do not know of any person who quilts 8 hours a day, 5-6 days a week, unless they are a professional (and even those folks set longer time criteria for themselves so their quality stays up and they don't feel under the gun of an immediate deadline to get it done).
Don't feel bad about how long it takes. The only thing that matters is how you feel about it, not how long it takes.