The double precision time since this frame started (Read Only). This is the time in seconds since the last non-additive scene has finished loading.
此为自加载上一个关卡以来的时间（以秒为单位）（只读）。
Double precision version of timeSinceLevelLoad. This offers more precision than a float or single value, particularly over extended periods
of real-world time. In almost all cases, use the timeSinceLevelLoadAsDouble equivalent over timeSinceLevelLoad.