This 1902 map reveals how completely the geography of Sandymount Strand has changed:
The white-circled red paddle is where Leahy's terrace used to meet the sand: "They came down the steps from Leahy's terrace prudently, Frauenzimmer: and down the shelving shore flabbily, their splayed feet sinking in the silted sand.... Like me" Stephen is also on sand, anywhere east, southeast, or even north or a little northwest of them. If they're facing northeast, "came down" may mean he's northeast? And could "Like me" imply he also just came down those steps?
Was there an 'Irishtown strand' north of ["Am I walking into eternity along"] Sandymount strand?
"Broken hoops on the shore; at the land a maze of dark cunning nets; farther away chalkscrawled backdoors and on the higher beach a dryingline with two crucified shirts. Ringsend: wigwams of brown steersmen and master mariners. Human shells. ¶ He halted. I have passed the way to aunt Sara's. Am I not going there? Seems not. No-one about. He turned northeast and crossed the firmer sand towards the Pigeonhouse."
If he's facing Ringsend while standing on sand, he must be facing west/northwest. Sara lives (we think) on Strasburg Terrace, northwest of Leahy's. So where's the "way" he's passed??? Was there a wall with stairs at Leahy's but no stairs at Strasburg? So could the "way" have been some stairs inbetween, or even northwest of Strasburg?
'Rose' (reg req) argues (I think) that "towards the Pigeonhouse" must mean towards the Pigeonhouse Road, and the turn takes place as Stephen passes Strasburg heading northwest from Leahy's, after earlier heading southeast from Strasburg to Leahy's.
'Rose' also tries to deduce Stephen's startingpoint by means of public-transportation schedules, which doesn't (alas) resolve the basic in-episode-path problem-- we still can't even be sure if Bloom's sighting occurs before, during, or after Proteus-proper.
The clue in Hades where Bloom spots Stephen from Watery Lane must be necessary, complicated by this additional passage from Eolus: "Wonder is that young Dedalus the moving spirit. Has a good pair of boots on him today. Last time I saw him he had his heels on view. Been walking in muck somewhere. Careless chap. What was he doing in Irishtown?" 'Rose' argues the muck could indicate Stephen arrived in Irishtown post-Proteus via the then-under-construction Ringsend Park. But lines-of-sight seem to require Stephen was very close to Watery Lane at this point.
Alternately, Simon's rant in Hades: "— Down with his aunt Sally, I suppose, Mr Dedalus said, the Goulding faction, the drunken little costdrawer and Crissie, papa's little lump of dung, the wise child that knows her own father." might synch with Stephen's imagining: "My consubstantial father's voice. Did you see anything of your artist brother Stephen lately? No? Sure he's not down in Strasburg terrace with his aunt Sally? ...The drunken little costdrawer... Crissie, sir. Papa's little bedpal. Lump of love."
In Eumeus, DB Murphy says his ship arrived at (roughly?) 11am, which seems to date the end of Proteus to just before this: "Moving through the air high spars of a threemaster, her sails brailed up on the crosstrees, homing, upstream, silently moving, a silent ship."
"along by the boulders of the south wall... The flood is following me. I can watch it flow past from here. Get back then by the Poolbeg road to the strand there. He climbed over the sedge and eely oarweeds and sat on a stool of rock, resting his ashplant in a grike... In long lassoes from the Cock lake the water flowed full"
According to the 1902 map, Cock Lake meets the boulders of the south wall at the Pigeonhouse, a mile from Leahy's steps. But the road back is always called Pigeonhouse road, never Poolbeg road. And Cock Lake probably shifted from week to week like Proteus...?
Could Stephen then walk a mile from the Pigeonhouse to Watery lane by 11:10am?