Tips for booking PEO slot

[OrangeCounty]

Hi all

I am looking to extend my T1 General, I've registered online but have not found any appointment slots.

I've read this sticky which was very helpful http://www.immigrationboards.com/viewtopic.php?t=72749

I was just wondering whether you guys have any more tips to successfully get a booking?

When should I start "stalking" the site?
If my leave to remain ends on 16th March, when should I aim to get the appointment?
Can I book the next available place (that is further) and cancel it later if I find another slot closer to home that becomes available in the future?
Is it worth to get an agency to book the appointment?

Thanks!

[OrangeCounty]

Anyone?