If I buy river stone shares right now, will I still to get the dividend? Is it still the time buy this share?

Yes you will still get the dividend since ex-d is in Jun. but note that price will adjust down after the ex-d date. so please do not buy a share just because of its dividends.

imo, riverstone has been undervalued with a fantastic balace sheet for a very long time and only recently ran up i believe due to this pandemic.

at current valuation, i don't think i will add positions. again, think long term whether can they still get such orders after the pandemic. will orders decline after pandemic when or maybe they will gain new customers from their competitors.

hope this helps