The batteries inside these lights are 4/3 A sized cells... doesn't mean a whole lot except that it tells you what they can handle in term of charge / draw rates.
4/3 A cells can be charged at up to a 1C (1*capacity) charge rate, which for 4500 mAh cells (4.5 amp cells) would be a 4.5 amp charge rate.
A 1C charge rate will charge your packs in 1 hour.
At 1.4 amps (about a 1/3C charge), it should take 3.5-4 hours to charge your battery.
At .7 amps (about a 1/6C charge), it'd take around 6-7 hours to charge your battery.
Do the different amp rates matter? A little bit...
High amp rate (4.5 amps) will heat your batteries up nicely, charge them quick, and maybe take a little out of the lifetime of your battery. You'll still get around 1000 cycles though.
Lower amp rates, like the .7 amp rate, are good for balancing out the cells in your battery pack. A 4.5 amp pack at 16.8 volts is made up of 14 individual cells, which probably don't charge exactly the same. If your batteries aren't performing like they used to, it may be useful to charge at a lower rate... although ideally you want to do it at 1/10 C (.45 amps).
The 1.4 amp setting should be just fine, and is a good middle road approach. You won't charge them super fast... which puts less strain on the batteries, and is less likely to create large voltage differences between cells.
If you notice your light's burn time isn't what it used to be, try the .7 amp charge, it'll probably get some of the burn time back for you.
Also remember that NiMH cells need to be run a few times before they start performing at their best... you'll notice that you get a little bit more burn time out of each charge for the first half dozen cycles or so.
Hope that's helpful... I have a bunch of experience with NiMH batteries in R/C racing / flying applications. The same rules apply for dive lights =)
-Brandon.
