Hello!  Newbie here, I've joined p411 and had my employment verified, and now and looking to set up appointment with a provider.  Since the p411 appointment request form includes time and date, how long, incall/outcall, and my contact info, what would be something to put in the personal message spot?  May be over thinking things but I feel like there's something that should be put there that I'm not thinking of.  Thanks.

Tell her whatever you want, something like I'm looking forward to meeting you or some such. Don't talk about sex or money in your little note.

general introductory details about yourself 'I'm 52 y/o, an avid cyclist, love reading books about {whatever}.'

Such as: "Hi ____, my preference is to meet at noon, but I could manage to meet at anytime before 5pm." or "I can also meet at the same time on the last day of your visit." You get the idea.

Like others have said you can put anything in the box or leave it a blank.
Most gents who contact me via P411 appt request put their hotel info in the message box and they might mention how they are flexible on time but just put a specific time so the message would go through.
Or if you are in town for a certain amount of days you might put in the message box you are flexible on the date of appt.
Yes,you are over thinking this a bit.If you don't have anything to add you could just say I am looking forward to seeing you and I hope to hear from you soon

I use the personal message area to introduce myself, let her know where I noticed her (P411, TER, or some other site) and as CP mentioned give her an idea of my schedule should the appointment day/time I requested not work for her.  No need to get overly wordy, but use it to personalize your request.  

Although P411 rules state that "appointments should not be requested through PM" I still find it easier to make an inquiry through PM first and then if asked to, I will then make a formal request through the "request an appointment" route.

Personally, i treat "rules" as "requests" and as long as I am polite, respectful, and most importantly "the one paying" I have no problems bending the rules just slightly. lol