Time gap

After attempting once, after how many days can I attempt elitmus again?

Once PH test released

Like if I give on 16th April, I can attempt again on 30th april right?

Nope if you gave the test on 16th april its Ph score will release on or after 10th may
So you may appear for any date after 10th may

Won’t the result get declared within 18 days?

No doubt they say it will take max of 20 days but I have observed, they take around 1.5 month