@ TrueNorth4Runner FSM has a very detail procedure for filling and checking correct fluid level. Needs fluid temp to be between 46C ( 115 F) and 56 C ( 130 F)for an accurate check w/vehicle at level. If you want or must have perfect fluid level, I'll suggest to do this. Jack up vehicle ( and level it ). Start engine and let engine idle to warm up tranny fluid. Take temp of tranny case. When it reaches 46 C remove overflow plug w/engine still running. If no fluid comes out, add .4 liters ( .42 US qts.) thro' refill hole. let engine idle for 10 secs and repeat procedure with overflow plug. When fluid comes out and slow to a trickle, install overflow plug, stop engine and you are good to go. If fluid comes out when you first remove o'flow plug after fluid had reach 46 C ( level was higher than desired ), let it flow till it trickles and reinstall o'flow plug and again you'er good to go.
Toyota claims that its WS ( World Standard ? ) tranny fluid is a lifetime feature and requires no drain/refills. This is another discussion/debate for another day.
From my personal experience w/my 05' 4R , when the line broke and drained all the fluid, what I observed from the old fluid ( coating the tranny lines and case ) , the color was still red and in good condition ( at 140k miles). After the rebuild the only noticeable difference came during upshifts in the winter months when the vehicle was first started. The upshifts were quicker as opposed to previous when overdrive did not kick in for another extra mile or two. Most likely the result of the rebuild and not from new fluid.
Yes, as AuSeeker mentioned, low or high fluid levels are not conditions you'll want in one's tranny.