SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b2d68fbd0841bc805ca95b8cf528761ada734e562566f753946115fce84a40b0' 
  AND token = '6LX5dL6GehX3qkR/wTYmKR+UkJUvDd7UFJKi/kZNCrM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00016

JSON explain

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