How can we make a timer system I already know we have one way of using it but I want to know about a more advanced one.

for i = 10,0,-1 do
print(i)
end

I know this is a way but I want to know how we can use another way of timers like if I wanted to have 1 hour,30 min, or other time I don't understand how to do it. I need an example of GUI and if statement example that I can use. The statement and GUI Timer would be helpful so i can understand better and use it.