"Bank and Shoal of Time", a novelette by R. A. Lafferty, first published in the 1981 paperback anthology A Spadeful of Spacetime (Fred Saberhagen, ed.), which can be borrowed (for free but registration required) from the Internet Archive. That must be where you read it "more than 20 years ago" as it seems to have been reprinted only once, in the 2017 Lafferty collection The Man with the Speckled Eyes.
Michael Main's summary from The Internet Time Travel Database:
Peter Luna brings five “time attempter” experts to his estate, hoping that he’ll be able to pass on his secret for getting over the time shoal that prevents them from exploring the past.
The invitation:
This was the message received by a dozen or so experts in the "time attempters" field:
"I have succeeded in establishing a creeping time-satellite or time-shuttle at my estate of Moonwick near Lunel in the Hérault Department of the People's Republic of France. If you are really experts in your field, you will appreciate the importance of this. From this time-shuttle, which is just beyond the 'shoal' of all of you to whom I am sending this message, it will be possible for you to launch genuine time probes. I am sending this to a dozen or so and I hope for acceptance by at least five. I must have a matched set of at least five. Some soon. A very little bit after 'soon' will be too late for me to transmit the shuttle to you. Bring ideas only. Everything else for frugal and break-through living is provided. You will receive various transportation chits and enabling papers. Peter Luna."
Peter Luna's foreknowledge of his death, and his "Socratic" demand that the visitors discover his time-satellite on their own:
"I am that Peter Luna, yes. I do not avoid that death. I die in 1928, and this is the very day that I die. That's why I've put this day on such a slow time-jog. It's my death-day and I'm not in a hurry about dying. And I want to transmit this set-up to the five of you before I die. And yet you have to come to the intellectual acceptance of it at your own pace. It's rather frustrating for me."
"What a cover story!" Annabella MacBean admired. "You're quite a spoofer, in addition to other things, Luna. But how do you (alive as you seem to be at this moment) know that you die on this particular day in long-ago 1928?"
"Oh, another time traveler told me. He discovered that I had a time-satellite here and he used it three different times. He had a lot of equipment to move into the past from this easy jump-off bank. In between my visits here he looked me up and found my death chronicled. I had the reputation of 'mad scientist' so I was noticed a bit. My clock, of course, stopped at the minute of my death. And the big house here was taken down or wrecked later. At least there were no signs of it in his day. So I die a little bit after noon today, and it's a little bit after noon now. And it may be that it will take the psychic kick of my death to transmit the realization of this set-up to you.
Peter Luna dies:
"Ah, I cloud over! What are these things around me? Five shadows, five voices? I knew them for a while, but now they dim out."
The aura of Peter Luna was quite visible, aided by the aura-amplifier of Rowena Charteris. It was a quivering and quaking loop.
It expanded suddenly, and the five persons stepped through it. It collapsed and extinguished itself then, and Peter Luna was dead.
And five happy-sad time-achievers went with lively step down the 'Road to Yesterday.' They could have gone down it five seconds before this, but it does no harm to fulfill a ritual even when it is rank superstition.
