This is not very specific, so the help you will get is not specific.
The 'period of time' will need to be defined somehow. If you are changing the value every second, when you change the value you should check if it has changed. If it has not, increment a variable. Once the variable hits a specific value you can turn on the LED.
At some point you will need to turn the LED off. Have you thought about that?
How do you want to scroll it? Left or Right? Do you just want to move it off the screen or rotate through?
You need to understand the << and >> operators in C - this will move the bits in a byte/word/long to the left or right by the specified number of positions. Scrolling is just moving bits the way your characters are defined.
Instead of send the midi messages out the serial port, try printing them out to the serial monitor of the arduino. This will eliminate the comms line and beyond as a source of errors. If the messages are right at that pint, then you know where to look. If they are not right, then it is all in the Arduino code ...