We were there last Sunday and Monday. It was busy. The Monday was actually worse than the Sunday, I guess due to insets, private schools having broken up etc. If we'd only had one day I think we would have cracked and bought reserve and rides.
We used the app to see when queues not as bad (although it wasn't always accurate ) and made a conscious decision to decide if we thought the queue was worth it or not eg we didn't go in the pirate log flume at all as usually 90 minute queues. I don't think we queued more than 45 for anything, although I wasn't timing as I think that would drive me mad! The second day we were there before opening and got 3 rides done in first hour, and then relaxed a bit more. It definitely gets busier after 11. I think we counted 16 rides between us in total over 2 days plus pirate show, 4d cinema, Ferrari building, miniland, mythica forest, drench towers, play areas etc, so I'd count that as worth it. They were full on tiring days though!
But if you are only interested in the rides, not exploring the Lego models etc I wouldn't bother this time of year. And don't have your heart set on one particular ride - there might be huge queues or some close eg we couldn't do viking river as it was only open a couple of hours the whole 2 days we were there.
Take food and drink so that's one less thing to queue for (we only bought ice creams there but took us ages!), And you can eat in queues or watching pirate show for time saving.
We LOVED Flight of the Sky Lion. Did that twice - the second day we ran straight there and got on 2nd ride of the day. With that the queues look long, and ride / changeover time is long, but they fit about 70 + people on at once so it moves quicker than it looks. Laser raiders a d the Ninjago rude were both things we were glad we did early in the day as the queues were really long later. The dragon was probably what we queued longest (twice ) for bit it was never more than an hour on the app and often a lot less.