To determine the length of a video you need to use the YouTube Data API. You can refer to this Stack Overflow answer, which gives an example of how to make a call to the API
For example the following call:
https://www.googleapis.com/youtube/v3/videos?id=9bZkp7q19f0&part=contentDetails&key={YOUR_API_KEY}
Gives this result:
{
 "kind": "youtube#videoListResponse",
 "etag": "\"XlbeM5oNbUofJuiuGi6IkumnZR8/ny1S4th-ku477VARrY_U4tIqcTw\"",
 "items": [
  {
   "id": "9bZkp7q19f0",
   "kind": "youtube#video",
   "etag": "\"XlbeM5oNbUofJuiuGi6IkumnZR8/HN8ILnw-DBXyCcTsc7JG0z51BGg\"",
   "contentDetails": {
    "duration": "PT4M13S",
    "dimension": "2d",
    "definition": "hd",
    "caption": "false",
    "licensedContent": true,
    "regionRestriction": {
     "blocked": [
      "DE"
     ]
    }
   }
  }
 ]
}
The time is formatted as an ISO 8601 string. PT stands for Time Duration, 4M is 4 minutes, and 13S is 13 seconds.
You can then use time.sleep(secs) to sleep for the number of secs returned from the API.