On page 1, the proximity sensing diagram, the IR would have a 38 KHz frequency. On page 2, it shows the demodulator receiving 30 pulses to create the output. So even if the output could update at 1 KHz, 288,000 ms are needed to take all measurements giving less than 4 Hz system response (and that's a very optimistic estimate).
Take a look at this type of ambient light sensor, i.e. the TSL12T Light-to-Voltage sensor has a buffered voltage output that can drive +/- 10 mA and wouldn't be susceptible to noise. Low cost and available at Digi-Key. Less than $1.20 ea (per 288 qty).