cameras. I make the call from that location 5 minutes before the date is supposed to begin. Once I have the room number I drive to the final location and walk in as if I am a guest, usually carrying a computer bag or something so I can blend in.

Keystone is so right about the parking lot too.
That was one of my first screw ups.
I parked in the lot about 15 min early, and just waited.
Just like key said.. I saw I was getting attention from guards.
I got out opened the trunk, and started fumbling through my stuff. They just drove by.
I grabbed a bag (which I never was going to do) and called for the room #.
Thank god she was ready! The bag helped me blend in too! Even though it was a gym bag.

What is funny about that the guards are not looking for hobbyist.
They are looking for thieves.

Try not to over think when to call, and stuff like that.
I do it sometimes, and it makes me nervous.
If I had to guess. 20 min early is too much.
Exactly when the date is supposed to start. Too little.

5 minutes before the date time.  I usually call for the room number when I am getting close to the hotel.  That way, I do not have to sit in my car in the parking lot.  Also, I tell her how close I am, and ask if it's ok that I am early, if I am a bit early.   If she says it's not ok to be early, then I will drive around and not sit in the parking lot.  There is no set protocol, but I think 5 minutes is cool with most providers.  

I generally have a Wal Mart bag with the gifts in it, which I hope helps me blend in.  It is extremely important to walk thru a hotel lobby acting like you belong.  If you have not been to that hotel before, you should ask her where the elevators are, so you don't appear lost.  If a staff member says hello, by all means reply, they really have no idea that you are there to visit a provider.

Swim

was once thwarted by a weather event that brought the highway to a stop.  Once I have located the call point, I withdraw.  Sitting outside a hotel readingthe paper is a good way to draw the attention of Hotel Security & Patroling Police.  So I withdraw to the corner coffee shop, timing my return.  If it's someone I've seen before, I'll call from the coffee parking & tell them where I am.  It once nearly backfired as the lady wanted to check me out the window...  quickly remidied via the gas pedal.  I try to arrive & call less than 5 minutes in advance.  
Agree, if you don't know the lobby layout, ask how to find the elevators so you don't look lost & have to interact with helpful hotel employees.

she will usually text or call you 5 minutes before your appointment..i now always arrive a half hour early..i used to do the parking lot bit but found it not to my liking..i just cannot see sitting n the car freezing your ass off and being scrutinized by security guards..most incalls are at nice hotels..i arrive early..check the layout of the place and head to the cocktail lounge for a drink..it relaxes me after the drive and helps you mentally and physically blend in..she calls after my cocktail and i am ready..sure beats running around looking for the elevators looking like a scared puppy dog..believe me..i can spot them a mile away..so can the hotel staff..some hotels will even give you free valet parking if you have a cocktail at the hotel lounge..works for me..no muss..no fuss..