SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21f1f25faa54f63de49f0906f34f114bee2f088e874debcaea6196103f1b698d' 
  AND token = 'NyKF9+ptNrGbrYx2IcNsXspyBW+n3/1if/JklVYzlN0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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