Whenever we add a timer in the start node of process model, it starts a process

On timer event, click on "Show advanced options" and then select New Expression.
Then paste this tostring(cons!YOUR_TIMER_CONSTANT)=tostring(totime(local(now(),timezoneid())))

Publishing a model with a timer start event always triggers that start event to fire and start a new process instance.
This is something that must be managed when using Timers to start process models in Appian. There are configuration options inside the Start Event that will allow you manage when the next process instance runs. One of the configuration options allows for the setting of a condition that must be met before the timer start event will fire. These can be used to avoid unwanted firing of process instances. See this link for more information: forum.appian.com/.../Start_Event_-_Timer.html

Too get around this issue on save and publish we immediately cancel the instance that was triggered on the save and publish.

As mentioned above, we manage our timed-start models by utilizing a Boolean constant in the advanced settings. This constant is always set to true, unless we are working on the model - flipping it to false before publishing will prevent the model from running, the model is promoted with the constant set to false and we flip to true once all work has been completed, then timed starts can resume.

@vipins Hi, I believe that a good discussion has been made at forum.appian.com/.../e-188662 and I would like to suggest to go through the links in the post and the suggestions made by other users in it. Hope that gives you leads.