Just an advice, if you have trouble tracing your program properly, then you may want to redesign it, or else you may end up with spaghetti code. In your case, you may want to try to flatten it so that you don't have to use GOTO/GOSUB so much.
I am using @label. To do it all in one line is too confusing. Unless you don't want rotation. On PTC, it was incremental system. On SB, it's keyframe system. Keyframes is more powerful, but it uses animation table, and that takes a while to set up.
Tick, tick, tick, tick...cuckoo! cuckoo!
Sprite animation is much more sophisticated this time around, but also much more inconvenient to set up. Used to be sprite based timer was very simple to do.
How long until midnight? Here's another OSP project. This time, it's a timer. How many minutes left until cuckoo time? Fun with Sprites Rotation Animation.
It varies. The basic concepts are readily understood. Some of the advanced concepts, such as Sprites, backgrounds, animation, and music, take a while to understand.
Turtle graphic is a drawing system where you tell a robot turtle to go forward, turn left/right and raise/lower the pen, drawing lines as it goes. Usually associated with LOGO programming language, used to teach children computer programming concepts.