The Time Stamp service is offered in the form of web services integration :

The Time Stamp is a service that is designed to be used from the various applications or services offered by public administrations. In this sense, to make use of the service, it is necessary to carry out an integration between the application or service of the user administration and the Time Stamp. The Time Stamp has a messaging protocol that defines what business requests should look like and allows the service's responses to be interpreted.
This modality requires technical resources from the body to develop web services. To facilitate the integration work, the following documentation is offered:

Related Content:

In what state is the registration of the Time Stamp service?

Is it necessary to authenticate with a certificate to use the Time Stamp?

Integration documentation – Validator and Time Stamp