It depends what you understand (or your "someone" means).
Does the person intend to celebrate Sunday's Mass on Saturday evening instead? Does the person intend to celebrate Saturday in the Octave of Pentecost? Does that person intend to celebrate a Votive Mass of .........
Until you know those things, your "help" is quite limited.
What you can do is this: look in your Liber Usualis to find the Propers for that day (June 10th in the Sanctoral Cycle, Saturday in the Octave of Pentecost) and be ready to provide whatsoever the interlocutor requests, assuming that it's possible.
Some places anticipate Sunday. I don’t like it, but it’s done. The Mass of Saturday really should not be said after 1st Vespers, because, even if normally I agree that it’s not allowed to anticipate Sunday, the fact is that with an Ember Day, or in this case an Ember Day concluding an octave which began on Saturday after the Vigil of Pentecost, one ends the day very strictly at the conclusion of None.
The Mass of Saturday really should not be said after 1st Vespers
Use this as an opportunity to start doing Vespers right before the vigil mass, if this is regularly occurring. All parties shall be (reasonably) happy!
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