It is true that some people notice quite dramatic changes even after a day or two (such as sleeping more soundly) but generally the benefits are steady and cumulative. Often after a week or so people notice that they seem to have ‘more space and time’. It could be that people notice what doesn’t happen, rather than what does and they may say: ‘I realized that before I learned TM I would not have been able to deal with that situation in such a relaxed way’.
Absolutely not. You are learning a technique, a skill that you can practise at home.
Actually on a deep level the answer to this is yes. Yoga means ‘union’, making the connection between (or unifying) the busy active mind with the deep silence within, and you can perhaps think of TM as the mental aspect of yoga. However it is not necessary to do any postures in order to benefit from TM.
This is quite an interesting question. We can say that there are three levels of life: physical, mental and spiritual. In this context spiritual simply means that it relates to the deep experience of one’s Self, where the mind is silent. To this extent it is a spiritual practice, but there is no belief system associated with TM, or any unusual practices.