Best time to apply for externship?

When is the best time to apply for an externship for next summer? I'm in a 2 yr. diploma program and will be a senior next fall. I want to participate in an externship next summer..but I don't want to apply too late..or too early.

So, when is the best time? If it's before December, is it ok to apply and then hold off on sending your transcripts until after they are posted?

Where are the best externships? Of course, I'm going to apply to Morristown and Overlook (who isn't??) but I will also be applying to Mountainside Hospital (since I have a job there as a nursing assistant) and I'm intersted in St. Barnabas..Beth Israel in Newark...UMDNJ..Hackensack..Somerset Medical..and probably every other hospital in the northern part of NJ!

Thanks for all of your input!

M