Q. 1. Is there a Church teaching regarding how long I should wait before eating after receiving Holy Communion?
A. 1. The Catholic Church teaches that Jesus remains present in the Consecrated Body (formerly a host) and Blood (formerly wine) as long as the "species" (appearances) continue to exist. That means as long as the properties such as the size, color, taste, etc... continue to exist in the bread and wine, Christ is present in the Sacrament of the Eucharist.
These properties cease to exist when they are digested because of the changes that occur during digestion.
The Catholic Church teaches that under normal circumstances, when the communicant immediately swallows the Body of Christ (host) when receiving the Sacrament of the Eucharist, Christ remains physically present in that person for about 10 minutes.
Therefore it is safe to say that 10 minutes or more is a safe time frame to wait before eating after having received the Sacrament of the Holy Eucharist.
Considering that about 10 minutes elapses before the Mass ends after the distribution of the Sacrament of the Holy Eucharist, it is safe to say that once the person has left the Church after the completion of the service, it is safe to eat.
The faithful are free to delay eating after receiving the Sacrament of the Holy Eucharist if they feel compelled to withdraw in comtemplative prayer.