With small engines, you can certainly go longer with synthetic based on hourly usage, but it's not a good idea to leave oil in for more than a year or so because of condensation and contamination. OPE engines have small sumps, so it's cheap insurance.
I use synthetic on everything since the early 90s after I read a story from a NSACAR crew who related that after running cars with synthetic when they open them up the parts looked like they never touched each other. So I never had a lube problem. Just saying.