Is there any way to know the amount of bitcoin wagered on PrimeDice in last X hour (e.g. 24 hour), where the minimum size of bet was Y BTC (e.g. 0.0005 BTC)?
No there are no such personal stats, only for most wagered and biggest bets.
https://dicesites.com/primedice provide some overall stats not what you were looking but still good to know.