The main problem with driftwood is that it will be full of water and can’t be worked with until it has dried out. If you have access to a log drying kiln, you can use this to dry it out to around 5% water content in just a few weeks.
However, if you don’t have access to wood drying equipment, you’ll need to dry it out naturally. This will usually take over a year to reduce it to around 20% moisture content, at which point it will be workable.
You need to make sure that as the wood air dries, the changes in moisture content don’t lead to warpage or splitting. To prevent this, seal the ends using wax to prevent splitting and stack the grains so that they are perpendicular to the wind. This will prevent the wind from blowing into the ends and drying the wood unevenly. Uneven drying will cause the wood to warp as it dries.