SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'f51691684f4184ff99313b58c503bdb6aa3591698d2b336c9aef88150413d895' 
  AND token = 'TNoAPYmEDVs7e6GdwXMv5JFipY9/VRjh+/GeQH8x5Nw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}