There isn't really ever a bad time to go to church. It's great to stop in and pray whenever the church is open and you want to spend some time with God.
Perhaps the best time is when there is a Mass being celebrated. We should all make sure to attend Mass on Sunday (Saturday vigil Masses count as Sunday) every single weekend. Along with that, we should attend Mass on every Holy Day of Obligation. Not only is this the first precept, or rule, of the Church that all Catholics are bound to follow, but it is also our way of obeying the Third Commandment to keep holy the Lord's Day.
Don't forget that the Catholic Church celebrates Mass nearly every day of the year, and it is certainly helpful for your spiritual life to attend daily Mass in addition to Sunday Mass. There are other great times to come to church too, such as when Liturgy of the Hours is being celebrated or during Exposition of the Blessed Sacrament (which happens at St. Mark on the first Wednesday of every month).
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