The specification primarly says that the other parameters listed in the datasheet have been measured after 24h preheating. Secondly it says that the sensor may show initial sensitivity and zero drift and should be continuously powered for best stability.
But it doesn't specify the drift amount or the response during the first 24 h. I suggest to make your own observations. According to other vendors application notes, SnO2 sensors mostly stabilize within several minutes. Review e.g. Figarosensor.com