SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '593831d4e60e9393f62fcce27e76675c555740a0c6b2d2e4a6c35739d1bb5fdf' 
  AND token = '8euPD2AV8b5hYWzZTjTWjPQL4pqjeVoLizwFLfvy4wI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00026

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}