Pandu,
The issue is with your wait activity (SLA Percentage Timer). Your first activity tells the Workflow to wait until 50% of the timer is reached. You have to account for that as you move forward to the other activities. So your next activity tells it to 'Wait 75 percent of SLA' after already waiting 50%. That means that it will not fire until it hits 125% of the SLA timer. Think of each of the wait activities as a piece of the whole and they all add up to 100% of the SLA.
So your first activity is fine. Your second wait should be 25%. That plus the previous 50% puts you at 75%. If you want another notification at 90% then your third wait would be 15% and then finally it would breach at 100%.
Also, might I recommend removing the 'Notification' activities and switch to 'Create Event'. This will give you more control and flexibility with the notifications. You can pass the stage or percentage as a parameter and use it in your notification.
This work flow was SLA record only Robert I took screen short regarding this SLA only wai im sending the SLA screen shot
I'm looking for the instance of workflow on the record it should have been running on. Grab the TASK_SLA that failed your use case, then click the Show Workflow link on the bottom of that.
EXAMPLE
That'll show something like this...
