We just did POTG a few days ago, starting in Bomerano. We wanted to beat the heat and the crowds. We took the first Circumvesuviana train from Sorrento to Castellemare Di Stabia. From there, we took the SITA bus to Bomerano. It took less than 1.5 hours and we were on the trail by 8:15am (after stopping for coffee and a pastry).
If you are considering this route, the early morning train was pretty quiet. The tabaccheria in Castellemare Di Stabia wasn’t open so we couldn’t buy bus tickets. Luckily and gratefully, the bus driver let us on for free. We hiked all the way down to Positano and caught the ferry back to Sorrento. Good luck and enjoy. It was a fun and beautiful day trip!!