The only way to truly know is to log your time. I had to start doing that for longarming because I was grossly under-estimating how long it took me. So I simply put a blank piece of paper on my bulletin board. As soon as I walk in the room I write the date and the time. As soon as I stop I write the time. Now it is habit and it takes less than a second to do it (I make sure to keep a pencil or pen right there as well). You could time yourself for one block start to finish. Even if you chain-stitch several blocks at a time, by clocking how long it takes to make one from the moment you make your first cut until you take your last seam. Then multiply that by how many blocks are in the quilt. But then you have to log your time for assembling the quilt, quilting it and binding it. Everyone works at different speeds so the only way you will get a fair estimate of your time is to take the additional few seconds at the start and end of every sewing session by writing down the start time and finish time. Try keeping a small notebook right next to your sewing machine.
You will be surprised at how quickly it becomes habit and that it only takes a second to jot it down. I suspect you will be very surprised to see how much time it really does take. Also, if you are a prewasher, don't forget the time and effort to prewash and prep your fabric.