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What voltage level is required to initiate the timer?
If it is just +5 VDC, you might be able to run the PNP sensor to a TTL type inverter gate, with the output of the gate going to the timer. Also, it may be advisable to add a pull down resistor to the input of the gate, in order to insure a positive gate level, one that switches distinctly.
If you could include an annotated sketch or circuit diagram of your problem and idea, it might be helpful.