英语翻译内容为--首次更换时间为100小时,后续更换周期为300小时.

我的理解为：运行100小时后进行首次更换,以后每运行300小时更换一次.译为：
The first replacement shall be done after operation for 100 hours,and the subsequent replacements shall be done at every 300 hours.或
It shall be replaced for the first time after operation for 100 hours and subsequently at an interval of every 300 hours.

The duration of first substitution is 100 hours, then every 300 hours.

First replacement should be done after in use for 100 hours, the replacement cycle after that is 300 hours.

The first replacement period is 100 hours and the subsequent period is 300 hours.