Is there any time interval to write a post? No, if you are making a post, there is no time interval, you can check the forum rules, there is nothing like a time interval
There is time interval that is coded as waittime and it is related to forum member rank.
Brand new and newbie members will have wait time is 360 seconds and after their activity point becomes 15, they will have more friendly wait time, as 90 - activity point, and it will reduce more when a user has more activity point.
waittime = 360;
if(activity >= 15)
waittime = (int)(90 - activity);
if(activity >= 60)
waittime=(int)(34.7586 - (0.0793103 * activity));
if(activity >= 100)
waittime = max((int)(14-(activity/50)), 4);