SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6346962a0273896527d668b30567829aa4cb19d11205535ece476d659648f427' 
  AND token = 'yu0ikE1eNjep8B1OP/PvJ/zwZtZ+YN82Behx9ZwxqVs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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