You will need to measure the frequency over a long period if you want good accuracy, unless you have a good frequency counter. However, you may not need to worry about the adjustment at all if you only want +/- 100 ppm accuracy (10 seconds per day)
The capacitors are usually around twice the load capacitance of the crystal.
The capacitors have very little effect on the temperature characteristic, only the initial adjustment. 32.768 kHz crystals are tuning-fork crystals and their temperature characteristics is -0.035 ppm/°C², centred around 25 °C
So at 40 °C, that is 15 °C from the centre, so the frequency will have changed by about -8 ppm (-0.035 * 15 * 15)