M theory is the more unified form of different string theories. The M theory works in eleven dimensions. According to String Theory subatomic particles that we see in nature, the electrons, the quarks are nothing but the musical nodes on a tiny vibrating string. What is Physics? If you want an answer from string theory, then answer is simple, physics is nothing but just the laws of harmony which you can write on vibrating strings. What is the universe? The universe is a symphony of vibrating strings. What is Chemistry? Chemistry is nothing but the melodies that you can play on interacting vibrating strings. According to String theory, we are nothing but just the cosmic music and melodies played out on vibrating strings and membranes. Obeying the laws of physics is nothing but just the laws of harmony of vibrating strings.
So if there is a double time universe, then you can walk in a room and see people frozen in time while you beat to a different clock. That’s a double time universe. This is called F theory but so far it is unknown that will this theory survive or not, but M theory in eleven dimensions is the mother of all strings and this theory works perfectly fine.
We have problems in dimensions beyond eleven, theories are unstable or they decay back down to eleven dimensions. Mathematics itself forces you to eleven dimensions and that is M theory. This is the theory of everything, there is more space in higher dimensions to put all the forces together. Four dimensions are not enough to put the natural forces together and when you expand to eleven dimensions then everything forms perfectly well.