If nobody in your house takes baths, the tub is taking up the most valuable space in the bathroom. Replacing it with a walk-in shower makes the room easier to use, easier to clean, and safer as you get older. But a shower is a very different animal from a tub, and the difference is all in what's behind the tile.
A tub holds water in a sealed basin. A shower has to shed water across a floor and down a drain without a single path into the subfloor. That means a properly sloped shower pan, a waterproof membrane on the walls and floor, and careful detailing at every corner, niche, and valve. Skip any of those and the leak shows up months later, usually in the ceiling below or the floor next door.
Plan for plumbing changes. The tub drain is usually in the wrong spot for a shower, and the valve often needs to be replaced or moved higher. Doing this while the wall is open is cheap; doing it later is not. It's also the right moment to add a niche for shampoo, a grab bar backing, or better lighting.
Expect a typical conversion to take one to two weeks depending on tile and glass. Ask your contractor how they waterproof, what pan system they use, and who handles the plumbing. If the answer is three different companies, expect delays between each one.