SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51fc38b23a1abff03df1ab680f57217ddcd0f57cb3f7524aff898f73c8cf2ec1' 
  AND token = '6w/wqZtBDjhVCD8/YqHRTb/kXDLZprbD5gC2buG//j4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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