<div id="session-timeout-warning" class="govuk-warning-text">
  <span class="govuk-warning-text__icon" aria-hidden="true">!</span>
  <strong class="govuk-warning-text__text">
    <span class="govuk-warning-text__assistive">Warning</span>
    <p>You must save these answers by {{session_timeout}}.</p>
    <p>
      If you don’t save, your session will time out for security reasons.
      You’ll lose any information you’ve entered on this page.
    <p>
  </strong>
</div>

<div id="session-timeout-warning" class="govuk-warning-text">
  <span class="govuk-warning-text__icon" aria-hidden="true">!</span>
  <strong class="govuk-warning-text__text">
    <span class="govuk-warning-text__assistive">Warning</span>
    <p>You must save these answers {{ "by {}".format(session_timeout) if session_timeout else "within one hour" }}.</p>
    <p>
      If you don’t save, your session will time out for security reasons.
      You’ll lose any information you’ve entered on this page.
    <p>
  </strong>
</div>

Add default text for session timeout warning
Add default text for session timeout warning

If the developer forgets to provide session_timeout to the template the
user should still see something usable.
