The latency will be about 20ms higher than a terrestrial pure fiber based internet customer in the same location as the earth stations. For example whatever the latency is from the north bend WA site to downtown Seattle (a few milliseconds) plus 20ms. This is a considerable improvement over the absolute bare minimum rtt ping time on a Geostationary based VSAT which is 492ms.

There are a lot of terrestrial wireline last mile access technologies that already introduce 15-25ms latency on the last mile segment. Such as ADSL2+ on old POTS copper wiring or a heavily loaded docsis3 cable network. That is just from the home modem to the neighborhood's closest network node.