Really, it's like 'how long is a piece of string?' Depends on if you bid on something in a hard to let area, or if it's a popular area, and how many other people are bidding. Also depends on how many people are on the list in your town/area.
My friend recently got a nice bungalow in a very rural area that is very pretty. She has been on the list for 3 years, and has been bidding fiercely for about 6 months as her landlady wants to sell. She is being kind enough to not put the house on the market until my friend gets a property though.
She has been in the top 6 or 7 people bidding for the last 15 times she has bid, and was in the top 12 for about 15 times before. For the last 6 weeks before she was No 1 and got offered her bungalow she was in the top 3.
The week she bid there was only 3 bidders according to the housing association, because it's a tiny hamlet with nothing there except 25 other properties. (No shops or public transport or amenities.) Though there is a village with a Church, a parish hall with events on throughout the year, and a pub, just 20 minutes walk away.
She said it's fine that there's no public transport as many places she (and her DH) have to get to, they need a car for anyway. (Work, family, and the like...) Everything they need (shops, buses and trains, GP, dentists, etc etc,) are 3 miles away in a small market town.
No-one can answer how long you will wait @nervynellyy but if you are coming 5th now, I doubt you will wait much longer.