You can use the little up arrow over the timeline to pop out the wide view timeline, then hover the mouse over the far left to see how far back it goes without having to change zoom around.
As far as space is concerned, first up, set your cameras to H.265 or H.264+ if possible, it's compression is ridiculous with no quality loss over regular H.264
Second, to find say, recorded time per GB we can do a little math on our own. If you log into your camera directly, it will have a setting for bitrate, usually in Kb/s. With a little plug and chug we can find that GB/Day = 0.011 x bitrate in Kb/s
For example, Wyze cameras stream at 1920 Kb/s so 21 GB per day per camera. My Lorex cameras are locked in at 4096 Kb/s so 45 GB per day per camera. You can set cameras higher than that of course, but about 1024 Kb/s per MP is a reasonable guess (25 fps)
This gives you a base estimate of 11 GB/Day Per MP. Full load 24 MP would then be 4 days/TB. I'm seeing much better than that with H.265 compression however. I'm seeing around 6 days/TB on my system of about 30MP, which is pushing it because about 10MP of those cameras are inside where there should never be motion, set to no detection (they're just recording for security purposes).