@gerald85, there are a couple of things to note in the warnings in the export window. The first is that if you are using morph targets, you can’t use optimize mesh as that would change the triangle list and break your morph target. We do disable that at export when we see morph targets, but just for a gut check, make sure to uncheck that box.
The second thing to address is that you have too many influences per vertex in your skinning. Babylon.js supports 8 bones of influence per vertex, and you have 12. This can produce unexpected results, but I don’t know if that would explain the timing issue. The other thing to look at is your animation frame rate. Maya defaults to 24 fps where Babylon.js is native at 60 fps. There is a conversion done, but converting from 24 to 60 is not straight forward and may throw off the timing of your animation. If you want to animate at a frame rate other than 60, I would suggest 30 as the conversion is much cleaner.
I would take the first steps of either reweighting or reskinning your mesh to have no more than 8 bone influences per vertex first to eliminate that warning. Then retime your animation in Maya if you are at any other frame rate than 30 or 60. Then export without optimize mesh checked. Make sure you don’t have any other warnings in your console window either when exporting, then we can take a look at the results and see what might be the next step.