You have set a very busy schedule for three days. Amsterdam has too many attractions of its own to be seen in one (half!) day. You might want to check seasonal temperature and tree-leafing out prospects before planning a four-hour bike ride.
There is no question that Delft is a special location, but for the sake of wasted time on public transportation, you might want to look into the older and more picturesque sections of Amsterdam (or Haarlem), and accept them as a substitute for the long trip to Delft. Alternatively, if you can incorporate Den Haag into your itinerary, you would not have to return to Amsterdam.
I think you will have to find a road-side bus stop (in the correct direction ... ) in the semi-rural area where Keukenhof is located, to get to Leiden. Then you have to find the rail station and buy tickets to Delft. It's also important to consider that every time you "change" a public-transportation vehicle, you introduce waiting-time. On the other hand, the Keukenhof Express busses are an efficient connection between the bulb show and Amsterdam. I went to Delft (for the entire day) on the train from Amsterdam, which is much faster and more convenient than going by way to Keukenhof.
It's not next door, but you might research whether it's easy enough to get to Kinderdijk from Delft to replace Zaanse Schans with Kinderdijk. (We had a car the day of our Kinderdijk visit, so I can't advise on that.)