SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '521c365eef9afa0ac123f0adc47e4cc6866f5f3bd4dc7d1c86fc6ab2950c2cb7' 
  AND token = 'PukAh7jTcPw1qgJxTeYNIiIV54Z+HhIVG/MA4PgzbcU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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