The splint is supposed to give you a mild stretch though you might not feel it right away. It should feel different with it on than off, I shuould think.
Use wedges and socks to get more of a stretch.
Also, I am going on what my splint is like, which has three straps, and keeps my foot in place without being a dictator. Your three strapper may be different. If your foot is pointing or escaping somehow that can't be good. Go for the greater stretch with wedges and socks, maybe while watching TV for an hour or so, to make sure you are not overdoing it.