I haven’t played around with it for more than a couple minutes after getting it to work just now, but if you are running a source version of the engine, you can try to change the length of the timer:
\Engine\Source\Runtime\ApplicationCore\Private\IOS\IOSAppDelegate.cpp (line 967)
timer = [NSTimer scheduledTimerWithTimeInterval: 0.5f target:self selector:@selector(timerForSplashScreen) userInfo:nil repeats:YES];
I would assume a similar line is buried in the Android core too.