On the Universalis site, I found rubrics and text for the Prayers of the Faithful.
After each intention there is a pause while the faithful pray. The minister says:
Lord, in your mercy.All reply:
Hear our prayer.The Priest concludes the Prayer with a collect. When the Liturgy of the Word has been completed, the people sit.
That must be the United Kingdom supplement, as the US edition of the Roman Missal has only this rubric:
Then follows the Universal Prayer, that is, the Prayer of the Faithful or Bidding Prayers.
Even Appendix V, which gives many samples of these, provides no rubrics whatsoever.
What do you make of “After each intention there is a pause while the faithful pray.“? This pause could be implemented easily enough with most any form I’ve encountered at a Mass in North America.
Sit in the purple chair, and render liturgist’s judgment. Would you implement this, if you could? How long would you train your deacon or lector to be silent?
Catholic Sensibility 
Technically, the very heart of the prayer would be that silent prayer of the whole. That’s hearkening to the form of the General Intercessions in the liturgy of Good Friday.
When I was in Ireland in the late 1980s, the form I found didn’t include “Lord, hear our prayer”. Rather, the reader of the intention would conclude with “Lord, hear us” to which the congregation responded “Lord, graciously hear us.”
An older practice with regard to the length of silences is to use part or all of a commonly recited prayer as a measure. For example, using the Our Father to determine the length of the silent prayer near the end of the proclamation of the Passion Gospels. And in offering verses of the psalms, various lengths of the Hail Mary’s opening phrase or more might be used to determine the length of the pause in the mediant cadence of a verse depending the resonance of the acoustic – the longer the reverb, the longer the pause.