Greg = 4.8A / 1.5 AH = 3.2 hours, if fully discharged. Since this charger has no metering on it, just a red LED when charging and Green LED when charged, I can't give you a measured response.
Here's how I operate my battery powered trains -
I run them until I'm tired of it, which is always before the battery discharges, unless I'm doing an all day open house. I usually run for 2-3 hours though. All of my trailing cars or tenders have charging jacks. After the run, I bring the tender or or trailing car into the garage where my charging station is. Plug in the charger. This is usually just before supper time. Then I check on it a few times during the evening, and it is usually done well before bedtime. So I'd say it usually takes mine about 2-3 hours at most. Next time I want to run, I return the charged trailing car or tender to the train shed and decide what I want to run. Everything in the shed is always charged and ready to go. (Note: I've even had a system sit out there all Winter long, and still be ready to run in the Spring (NiMh). Not a full charge left, but runnable. And yes, sitting out all Winter is probably not doing the battery any good.)
I always hear guys saying they don't have time to charge batteries before running their trains. Neither do I. That's why you do it AFTER you run trains. Stan swaps his out. But it's the same difference, just charge after use.
By the way, I charge my NiMhs at C/10 (10 hours for a full charge), so the Lithium-Ion seems fast to me. It doesn't really matter how long it takes. I'm off doing other things.