Right now, they are still working through pre-trial issues. There is an evidentiary hearing May 28 which is the next docket date. They are arguing what should and should not be allowed as evidence. Zimmerman is also appealing the court's order that prohibited him from taking a deposition from Ben Crump who is the Martin family attorney. That decision may be released today as that court releases opinions on Friday.
Starting June 10, they will start picking a jury, which should last at least a week - maybe even 2. The trial itself will probably last 2 weeks. Those estimates are from the last couple of status conferences.
The court was fairly adamant that the schedule would be upheld unless something extraordinary happens. I'm guessing that the defense will get a week's delay if they win the appeal. Zimmerman is also asking for a delay if the voice experts are admitted, but that is unlikely, IMO.
Some resources to get a basic idea of the issues at hand:
George Zimmerman Legal Case - the website of Zimmerman's legal team. It posts motions and orders fairly quickly. If you're looking for filings that aren't in the main page, look at the links in the right margin under @GZLEGALCASE.
18th Circuit Media Advisories - the court's website for this case. This include all pleadings, but does not include discovery (evidence) exhibits. There is often signifigant delay in items being posted here, but once they are posted they are easier to find.
Seminole County Clerk of Court Docket for Zimmerman - this is a real-time summary of events in the case. This page will show events as they are entered into the system. It's a great place to see if anything new has been filed, but it is summary only - they don't post the text of the pleadings. It also reads bottom-to-top for each individual entry.
5th District Court of Appeals docket for Zimmerman - a list of appeals for this case.
Axiom Amnesia - a decent place to find most of the evidence exhibits. It's sometimes hard to find specific items. The first two discovery exhibits posted there contain ~75% of the evidence in this case.