One of the unspoken changes in Super Mario Maker’s version 1.40 update on March 9th, 2016 is that the initial appearance of a Piranha Plant from a pipe had its delay cut by about one second. This applies to all game styles.
This is apparent when viewing an older level. In one level uploaded on January 16th, a pipe in the first screen houses a Piranha Plant. Shown above, the Piranha Plant first appears about one second after the timer begins.
Older levels keep their pre-1.40 update timing when downloaded. However, making any edit to the level, such as adding coins, will transition the level to using the most up-to-date timing. At the time of this writing, that means the Piranha Plant will appear immediately at the start of the level.
The timing applies to pipes farther into the level, as well.
When walking along underneath the floating pipe in this level from September of 2015, Mario is four tiles past the pipe when the Piranha Plant first shows itself.
Following the update, Mario is barely under the pipe when the Piranha Plant comes up. At Mario’s walking speed, the Piranha Plant appeared five tiles sooner, about a one second difference.
If you update an older level, be sure to take into consideration the updated Piranha Plant timing.
If you have any ground-level pipes that enemies were originally intended to walk across before the Piranha Plant first appears — the difference in timing may cause the enemies to bump into the Piranha Plant and turn away.
Another consideration is levels designed for speed running. Typically a fast player should still be able to clear any pipes before a Piranha Plant appears, but you’ll want to speed-run it a few times with the new Piranha Plant timing to ensure the change has not impacted the flow of the level.