SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6b356fd4586135187d18acea909d2240ced845bfacea25df088eaa98aa609139' 
  AND token = 'bx+oJq+ErKFywDkj1sQ/oY+2+XJ2WVoG5EVPNgQ8dZs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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