Nowadays – not that much longer than watching the game itself, if the footage is good, of course. Maybe x1,5-x2? I rarely do those in one go, it’s usually a background task that I come back to during a day multiple times. Shesternyov’s one probably took about 120 minutes – I know the player well, footage is great, his role is super clear... the last one took a bit longer as I did all three of Baxter/Law/Seeler in one go, but again, footage was clear and all players were clearly recognizable... I’ve looked at replays for way too long though, especially on Baxter’s, looking for patterns of play and simply enjoying it, so it was probably around 2-2,5 hours in the end (the footage itself was around 60 minutes, they sometimes cut all the “boring” stuff out of old games before showing them on TV, sadly; 60 minutes gives you a fair assessment of the game though, especially since they usually cut out the bits where the ball was out etc.).
If the footage is poor or I want to watch replays for other reasons, it can drag out almost indefinitely though.