SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '81b543ea65dd48f6bdcea0d08fb713d738feb45f1322358fd1a42396db99f46a' 
  AND token = 'xBmGhonzjL+bMSoe4gdzLyFlFiHtrOp7lrMgViYt2Tk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00072

JSON explain

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