In order to make everything match up they push the timeline further back. But in order to do this it appears as if they had to assume that secular scientific findings are mistakes. This is a huge assertion and a bit more of a stretch that I am willing to make.
Another problem that I have with conservative investigations is that they start with the conclusion! This is not genuine methodology. Indeed, one conservative investigator who is interviewed in the film admits his bias.
I myself am open to the idea that some type of exodus occurred, but that it most likely did not occur the way that it is portrayed in the Bible. The problem that I have with the documentary is that it attempts to portray mainstream scientists as some sort of nefarious cabal who are hellbent on disproving the accuracy of the Bible.
To get the other side of the story, I highly recommend the following books:
The Bible Unearthed, by Finkelstein and Silberman and Who Wrote the Bible? by Friedman.