I think I know what is happening. I have this problem with one of my new projects that I'm working on. Because when the project is started, all values are set to 0, which means some blocks read this before other blocks set the values etc. Maybe you could change it to 25, so when Time Time = 25, set invisibility percent 100. The other way you could do this is if you have a 'when the play button is pressed', have a 'repeat forever' block having a 'check once else' in it. Have check once if Time Time = 25, then set invisibility to 100. In the 'else' section, put 'set invisibility to 0'.
Hope this helps, I'm not sure since I do not know how you got this command to work. Give it a try!
Update: never mind, misread what you said. But this may be helpful for someone else.