Had the same questions myself. I'm far from an expert on the matter, but I did manage to figure out a way to determine charge times that work reasonably well for my purposes.
I recorded the voltage at the batteries with them 100% charged with the PD9260C in boost/bulk mode. I usually get a voltage very close to 14.4v. To establish a baseline, I purposely discharged my batteries to 50% (12.2v) with the converter turned off. Make sure there's no load on the battery when you make the 12.2v reading. Again, with no load on the system, I turned on my PD9260C in bulk/boost mode and recorded the voltage. At the start of the charge the voltage on my TT is typically 13.5v - 13.6v (YMMV). I made voltage readings every 15 minutes until the voltage got very close to 14.4v. Using these readings, I'm able to determine (accurate enough for my needs anyhow) how long I need to run my generator to obtain a given state of charge. Note, if you load the system during the charge (appliances, lights, etc.) it will lengthen your charge times vs. a charge with no load.
I'm sure those with much more knowledge on the matter will chime in more accurate ways, but this has worked reasonably well for me.