I would only make a 2 to 4 min sequence and then schedule it to repeat for as long as you want. If you want to do more effects than you can fit into that sequence make a couple of sequences and put them all in a playlist that repeats. Trying to do a really long sequence will be problematic in memory usage, load and save time, etc.
You set the sequence time when you create it. If you have one started there are ways to extend the time, but if you only have 30 sec I would start over rather than trying to extend what you have.