SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '78acdbbc65d9a04f11a42c13108c123837797a1570a47e466235152f8ee416af' 
  AND token = '6jLMFhAFwedWjjycOePTMlMb6PusmbxvYiM1pBxb/2w=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00031

JSON explain

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