Good plan ... because like coasting indicates, trying the longer distances before you do something like a century is not necessarily about building up the strength to do the distance, it's about other things as well.

Bicycle fit is one issue. Your bicycle may feel good for 30 miles, but when you hit 50 miles and more, you may run into problems.

Knowing what to eat and when is another issue. Sometimes when people significantly increase their distance, they run into digestive issues ... nothing sits well, they end up not eating enough because they feel sick, and they bonk. Gradually increasing the distances gives a person time to experiment with what works and doesn't work.