I have a worksheet with ~12 million marks from coordinates on the map. When zooming in and out and using the performance recorder the times displayed for computing layout seems to be much lower than what I'm observing. I am waiting until all the changes have been completed and the image is completely rendered. It seems like the recorder stops recording time as soon as the initial load is completed (even if the change isn't displayed yet). For example, the time recorded will be ~11 seconds, but I observe that it takes ~40, which is a significant difference. Not sure whether this varies by computer..
Any idea how the times are recorded? Or if this behaviour is expected?