How long after installing dialysis port you can actually have a dialysis treatment?

Immediately: Once its location is confirmed by xray it can be used for dialysis.

Varies with type: A-v fistula where a vein is connected to an artery has to mature. This means the vein slowly enlarges with the use of tourniquet, and exercise to the point where dialysis needles can be inserted, often weeks to months later. A-v graft fistula where a artificial graft is placed between the vein and artery can be used earlier within weeks, after swelling has diminished. Ask your nephrologist

Immediately: If you are talking about a temporary port placed under the chest wall then it can be used immediately.