Check this, tried to film it. This is in S mode with a 1/160sec shutter speed. You can see me pressing the shutter and flash firing quite a bit later. Like I said, this only seems to happen in PASM modes. When I set the camera to Auto or in one of the scene modes, flash (both internal and external) fire immediately like they should. It seems like (in low light) the a6300 is doing some additional metering before firing off the flash which takes some time. This is something the a6000 does NOT do, but I have no idea which setting it could be. I went over all settings and really cannot find anything that could explain this.
This happens with all lenses, tried the Zeiss 24Z, Zeiss 16-70, SEL50 etc... Always same behaviour. When using the a6000, completely different results and flash fires in an instant. It's very apparent that the camera seems to be doing "something". After acquiring focus and pressing the shutter, the screen darkens a bit and then flash fires and picture is taken. Might be some metering setting but I really cannot begin to find it. Also tried setting ISO to a fixed setting, same results.
This is the 2nd a6300 I try, so it cannot be a fault in the camera.
I want to add something else. When changing flash mode to "fill flash", "slow sync" or "rear sync", this does not seem to change anything at all. The flash behaves exactly the same. I always want to add that when setting the AF mode to "wide" the flash seems to fire pretty fast and behaves like it should. But when choosing a different focus mode (center, flexible etc) it starts to slow down. Maybe some setting where the camera meters for the selected AF point causing the delay? In auto mode, focus is also "wide" so that seems consistent.