Being 'psychologically ready' for TT, night or day, is not really supported by science, and is more a popular construct we've created after nappying took over from the child's natural awareness of the urge to let go, and, next, the ability to 'hold on'. They are two different things. With DS I started with the awareness of 'letting go' at night, THEN let him grow into his ability to 'hold on'.
An important thing is not to use dehydration as the method for 'night training', though. This is not training anything, just, well, dehydrating. It's a popular method, but I was never comfortable with using it - DS was still breastfed before sleep, and often through the night after 2.5 years, so I can attest to being able to learn night-continence without dehydration. In fact, DD has been night-continent and continence-aware for a long time now, and has just turned two - she stirs into light sleep and if she needs to wee she gets up and goes to the potty (in our set up it's too hard to ask her to climb up the step into the shed where the composting loo is, which is too high up for a step seat!!). And, definitely breastfed over night and breastfed to sleep - no dehydration required.
Brauer goes through all of this, making it a lot easier to understand and seem quite achievable
Aldo, it didn't take long with DS before I wasn't carrying him anymore and was just guiding him, then just whispering to him to go to the loo. We also went through bouts of resistance that we just rode through - it's not so much about the end result as the process that ensures a more lasting and happy outcome