SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '18d614cd232a78b434e529800e8a572c9c701a49ebaaadd73219a45e44f404f0' 
  AND token = 'blOIx+94RhTKE6GQLrwhsjamtV646oDXiFpiBHWzzmI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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