Which image format will allow my application startup faster, BMP or JPG?
Most of the time goes to disk activity to load the image. Then for this JPEG can be smaller and hence faster. However, for the presentation the pixel values are needed, and the BMP (if it's not compressed) has those directly, while the JPEG needs to be unpacked. I suspect those that there's at least an order of magnitude difference between those times, so that disk access time completely overshadows the unpacking/presentation time.
That said,
this time is likely so fast anyway that the user won't be able to see any difference, and
if you want more than hunches and gut-feeling (even if based on experience), MEASURE!.