The stock motors in my Losi box lasted over 18 months, and this last year it ran off the Losi 14.4v Lipo pack. I lost count of the number of Dynamite, GRP, and OS engines it broke in, my own motors and numerous other guys' here. Never had to heat up an engine to break in...
You can not push down and hold with this box, and you really shouldnt with any box anyways. Guaranteed to burn up the motors. I just bounce mine off the wheel quickly about 5-10 times, and they fire right up.
If your engine is new and has too much pinch, you should be loosening the plug and let it spin with no pressure. It does no good to put the ignitor on the plug, and press down and hold for 13.5 minutes, and let it just turn over without firing. If the engine doesn't fire right away, something is set incorrectly.