SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '294908e5baac329316ddd64810017807eabd592a481be979a5c053241571ca52' 
  AND token = 'a2gfwBIawi6U+i7pVvAWOHTyLVPk8GsDSfCGNb/+UoI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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