The is no rigid rule for laymen, the only rule is to do as much as you can as taught by the parable on the talents. If you read Christian morality, you will see that the "rule" recommended to laymen by Saint Nikodemus was to go to church twice daily in the morning and in the evening (which supposes vespers and matins), and if this was impossible, to use as substitute prayer at home. He talks about Jesus prayer but I guess that then, people did not have liturgical books at home. His recommandation was to pray 2 hours a day (for anybody) since the 22 other hours were dedicated to the body.
I am not judging but simply stating that attending heterodox services is uncanonical and spiritually dangerous. Those who do not agree with this can complain to the authors of the canons or give better ecclesiological argumentation on their opinion instead of launching accusation of judgment etc. It is the consequence of basic orthodox ecclesiology that teaches that praying with others has as prequisite sharing the same faith as them. People's laziness do not allow to break the canons and pray with heretics. They are to make violence to themselves and force themselves, which is anyway very often the case when you are to pray because the Evil is there, inviting you to spend more time in bed, watch TV etc. You do not avoid a temptation going into another sin... or doing something incorrect.