Ongoing Energy support (instead of single Transmission)
Do we send Energy while they are Meditating?
How long and how often?
Should the frequency vary, i.e. according to whether they are apparently doing well or not?
Is there any Further guidance?

We’re happy for you to follow any protocol that works for you, and for any others who wish to send Energy in this way.
You will find that one size doesn’t necessarily fit all, so it may not work with a large group of Meditators.
For someone who is very focused and keen to progress, it is good to fix a time to send Energy, maybe two to three times a week, and keep a check on their progress.
With people who have been Meditating for a long time and are sitting down out of habit rather than from a desire to progress, send Energy just occasionally.
Generally, it is best if Meditators ask you to help them Spiritually. They will then appreciate what you are doing for them and will be more likely to progress

Is it necessary, or preferable, that Meditators know exactly when Energy is to be transmitted? Do they need to be Meditating at that time?

As per the answer before, you need not be rigid in this. The Meditators going through a State would need to know, but use your discretion with this.
However, if you are sending Energy generally to people, be guided by how you feel, and also by whether they ask for help or guidance.
Be aware that everything is Connected, and people will come to your mind who may need help to progress.