Absoloutely. I pee into a measuring jug (it doesn't get used for baking any more!) and I'm pretty much on top of what to expect now in terms of capacity. Also helps to monitor urine colour and how much mucous is being produced. As said elsewhere, a dark coloured pee can indicate an emerging urine infection.
Tim makes some good points. The rule of thumb is that neobladders should be stretched enough to hold btw 4-500 ml and not much more, there's a danger of stretching it too much and ending up with a 'floppy bag' syndrome and that's not good.
Many people are told to measure output during the recovery period in order to learn what to expect, how it feels, it's all new. And there is a serious learning curve. Keep asking questions and learn all you can. Ask your doctor if he hasn't discussed this with you about how often to void, etc.
I'm 8 weeks out from same and I was told by my uro-oncology nurse to watch for backpain as an indication that the neobladder was full. I'd call your medical specialist on this one if you are worried but that's what I was told. My neobladder started with a 50ml capacity which isn't a lot and I guess, depending on design, yours will be similar. I'm up to about 250ml now, emptying at 2.75 hr intervals.
I am 6 weeks out from RC/Neobladder for T1/G3 & CIS, and things are going fairly well. Catheter came out at 3 weeks. However, for about a week now, I have noticed intermittent lower back pain/ache, but otherwise no suggestion of infection (fevers, feeling unwell etc.). Is this common? I had un ultrasound scan which ruled out a 'fixed' obstruction. My feeling is that this may be related to the still small neobladder filling, and the increasing pressure giving rise to a bit of reflux back up the ureters to the kidney. Is this backache common?