THIS IS AN ADVANCED OPTION
As it can be tricky to write your own scripts, and because ACP planner is somewhat archaic, I'm going to let you in on a little secret. Before I do, however, if you haven't yet, please read our FAQ on Script Writing here.
The best way to do this is with a hidden directive called "chain".
Use the web-based script planner (http://www.itelescope.net/reservations) to write your script for example, the M51. as a stand alone, perhaps as "M51.txt". Then use the generator to generate a separate script for your second observation. Let's say you called it: M51-2.txt
Now, use the "My Plans" section in the iTelescope interface to download your M51.txt plan. Edit the script, and add only one line to the end:
Save it, and re-upload it under the original file name, and you're done.
An example of this in use would be there two plans:
M51 13.4983 47.2
M51 13.4983 47.2
This will result in only one minor annoyance -- your receipt will not include the log for the M51 images. (You will be billed, but you won't see the log itself). You can review the log any time by using "My Logs" on the web.
Note that you can chain an unlimited number of scripts in this manner.
As to billing, yes, you are billed only for the time the shutter is open on your target. You are not billed for slews, focusing, or centering exposures. The exception is that there's a minimum billing amount for a scope (usually a few points), so that science users can't do 30 exposures of 10 seconds each, and be billed for only 5 minutes of time when the run will take well over an hour.
Actual time to run a plan depends on the number of focuses, the number and binning of images, and the duration of your exposure time. A good rule of thumb is:
Total imaging time +
7 minutes for initial focus/slew +
1 minute per image taken for readout/calibration +
30 seconds per image taken for dithering +
5 minutes, general error (2nd focus star, reservation start delay, etc.) =
Total reservation time
If using periodic focus or periodic point, first determine the number of focus/pointing runs by taking the Total reservation time from above and divide it by the interval you set for periodic focus/point, and subtract 1. (IE: if you choose periodic focus and point every 30 minutes, divide Total reservation time by 30, and then subtract one from that answer, as the initial focus/point will happen automatically.)
For each periodic focus run add 3 minutes
For each periodic pointing run add 4 minutes
This will very nicely approximate your total session time, which you can then use to determine your expected end time.
Fine Move Method - NEOs, searches for comets etc. No Tracking.
With the exception of T27, none of our systems have a rotator and have a fixed PA, so this cannot be adjusted. We also have #manual deactivated on all of our networked systems as our community has many members with very different levels of experience and no real way to define which users are experienced enough to handle manually slewing a system without damaging it.
So, to prevent this damage, the only solution is to eliminate the possibility.
What you can do, however, is use #trackoff and point the target directly at a specific RA/DEC, image, and in the same plan (without the use of #chain and henceforth without additional plate-solve/corrective slew) enter a second target with #trackoff and a new RA/DEC: As a simple example:
mytarget 11.77 +5
mytarget 12.33 +10
This script will have the system perform an initial plate-solve and then corrective slew to RA 11.77 DEC +5. Next, it will take 3 x 60 Clear bin 1 images and then slew direction to RA 11.77 and the DEC 12.33 +10, at which point it will take 3 x 60 Clear bin 1 images - note that there is no platesolve or corrective slew between targets, and with #trackoff in use, the system will not track any stars - holding it's position for each session.
You can also keep tracking on for this, but you will have drift in the position based on the target - either way, this may fit your requirements.
We do offer this type of full manual control you are looking for in privately hosted systems.