Yes, try to join the Group Rituals as they are more powerful, of course. But if you cannot join the Group Rituals with your current schedule, then do the Ritual alone whenever you can.
It is best to do everything at the scheduled time, if you cannot, it is important to do it on the dates indicated, regardless of the time of day - here we follow the "day" as from sunrise to sunrise, not from midnight to midnight.
The God Rituals always work so long as you follow the procedures. There is something different when doing them together as a group that we always recommend others to join us in, but not matter what the Gods are always with us and these rituals always connect us with them.
Group rituals are more powerful, when you experience it you can really feel how the energy is different when performed all together, but it's also totally ok to perform them on your own if you can't at that specific time the Gods are highly understanding and will not get upset for this