I think this is simply a transition period for both of you.
It sounds like you have already done things to ease him into this new situation - teachers, kids, schedule, etc.
I think you should just drop him and go at this point. The teachers will let you know if there are any issues like long term crying, anti-social behaviors or major meltdowns during the day.
This period is as much about him learning to adjust to his new schedule and environment as well as it is for you to learn to let go and let other trusted adults handle things.
I know it's hard for you both. But I sincerely believe the longer you linger or don't stick to the same schedule the rest of the kids are on, the more he will fuss and look for you. Afterall, YOU are creating a pattern for him where you show up early, before the other moms. Preschool teachers usually say something like, "Mommy will come back after storytime," (this is a common answer for anytime the kids ask for "Mommmy".) This teaches them that there is a schedule, and that the teacher is telling them the truth...Oh look, it's after story time and there she is!!!
The more you linger at drop off or show up early the harder this transition is going to be for him. Try "talking up" preschool on the way there. Like "I bet you're going to have lots of fun with your friends today!" Then when you leave give him and hug and kiss and say, "I'll see you after storytime, have fun!!!" Be upbeat and happy. Wave goodbye and LEAVE.