If you aren’t serving alcohol there is really no notification required though it would be nice to let your guests know via word of mouth ahead of time. If you are only doing cocktails and hors d’oeuvres, it is best to use the word cocktail before reception on the invites. Also you will want to set the event during cocktail hours, say 4-6pm or 5-7pm. Plan for shorter reception including cake cutting and always have it end before 8pm so guests can make other dinner arrangements.
Countless questions come up when planning your guest list and reception and sometimes there is no clear cut answer. Whatever you choose to do, stand firmly by it as it is your special day and exceptions hurt feelings more than setting boundaries. Follow the old rule and treat your guests as you would want to be treated and relax and enjoy.