SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '34503eb5bb61f4be852eba2ec2423d51dbec4e6f37a6f6a5a28678a56faccb20' 
  AND token = '6+WuZtVHBMuuZsS7QgkqUj/JjpZCvWt7CfzQjK52iEc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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