SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '90d21004e571740b601a74188584035111730d033f2f8aecd4e137f0543c72e1' 
  AND token = '8mr+kvrbmaA628Z1Puc/7teeybJkUCLNKbDniKGvSmU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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