What one would typically do is have a list of the patterns one wants to display, a list of intervals each pattern is displayed (if they are not all the same) and an index of how far in the list you are. When the elapsed time hits the current interval:
Increase the index.
If the index exceeds the number of patterns, reset it to 0.
Display the pattern at the new index.
Set previousMillis to currentMillis.
Set 'interval' to the interval for the new index.