Do I need to see the date when I go to Qianfo Mountain to worship Buddha?

No need. It doesn't depend on the date to worship Buddha in Qianfo Mountain, but because there are special auspicious days on certain days every year, some people will determine the date to worship Buddha in Qianfo Mountain according to the date. Every year, there are important festivals such as vernal equinox, Long Summer, Qixi Festival and Mid-Autumn Festival, so Qianfo Mountain will be more lively, and worshipping Buddha and praying for Guanyin will be more grand.