It is true - the process is called habituation. It depends on how frequent (odor exposure [or sniffs] per minute) a smell is registered. Habituation can last from less than ten minutes up to at least 30 minutes (Chaudhury et al., 2010). As mentioned in the link, different parts of the olfactory system appear to be involved, but it is mainly explained through receptor activation on the cell membrane of neurons. There is a limited number of receptors that wait for signaling molecules or odorants (odor molecules) to attach, much like the game musical chairs. Habituation is thought to be more a product of receptor activity at neurons that transfer the information than sensory neurons that receive the odorants. With time, receptors go back to their original states.
Whether this differs by scents depends on several factors. There is great variation in individual scent acuity (see Kandel et al., Principles of Neural Science (5th ed.), ch. 32) from human to human, but frequency of exposure is a likely candidate, as well as salience - how strongly a smell affects us. We are more sensitive to smells that provide an evolutionary benefit by promoting survival, such as the smell of a burning forest. Perhaps habituation is less likely if it does us more harm than good.