Game Dev Tycoon and Game Dev Story both contain hours of playtime.
The challenge comes when you need to keep the player interested that whole time.
those 2 games i think are closest to a perfect tycoon game, there are some more things to add to them, but thats more expansion then actual system improvements, their system in my opinion, is perfected to a high degree, if you can come as close as them in your game, then your on the right path
tycoon games are a odd choice to program, its not that its to hard, its actually simple do A to get B if C = D its the most simple game u can ever build, however as Kuzie said, you have to get a gameplay that doesn't boredom's the players.