SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50536f75b6d0a242dece344dc2a8c39c2609f766c38acbc52b60c3cc48b5b1ad' 
  AND token = '+IuwdoJJpVBE9qGzaLR+KOe+pnLsNjw3EvTQ6miazLQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00017

JSON explain

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