You will have to make a call to the YouTube data API's video resource after you make the search call. You can put up to 50 video IDs in a search, so you won't have to call it for each element.
https://developers.google.com/youtube/v3/docs/videos/list
You'll want to set part=contentDetails
, because the duration is there.
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.