It all depends on what band you are in, how many bedrooms you need, and what you bid for. If you are in the top band you should wait only weeks or months, in the second band your wait could be around a year, but in the third band it will be a lot longer unless you are bidding for sheltered flats, for which the wait is usually no more than a year or so.
If you place restrictions on what you are prepared to accept, your wait will be longer than average. For example, if you bid only for houses and not for flats, only in private roads and not on estates, only for council and not for housing association homes, or only for 1-beds and not for studio flats, you will wait a lot longer because you are competing with more bidders who are also attracted to these kinds of home. The more bedrooms you require the fewer properties we have available. If you need disabled adaptations you may have to wait some time for a suitable property to come up, even if you have been put in one of the top bands.