How long does it take to get use to dentures and to start talking clearer?

Varies: For some people a couple of days, for others, a few weeks.

Different for all: Dentures are custom acrylic constructs of ones pink gum tissue and teeth. They rely on the suction created by the surface area of the remaining gums, viscosity of the saliva and relief from the muscle attachments. Almost always the full palate is covered and the tongue can feel impinged. Each individual adapts differently to these circumstances. Most learn to tolerate it and learn to eat again.

Dentures and speech: There are many factors to consider to answer your question. First , is this your first denture? If so, it will take time to accommodate. If your denture is too large or bulky in areas this will also cause speech issues. Sometimes a lisp can also occur as the denture has not been properly adjusted. If this is not your first denture, I would think some adjustments are indicated.