(schematic) Using a micro controller to drive Opto-coupler > 555 timer > MOSFET
The OPTO's emitter should be grounded, and the junction of its
    collector and R3 should be connected to 555 TRIGGER.
the formula for determining the 555's timeout is t = 1.1RC, so with
    45K and 0.1\$\mu\$F in there, the the output pulse will last for 5
    milliseconds, not 500.
The 555's output can be connected directly to the MOSFET gate, so
    you can get rid of R1, R2, and the 1N4744.
Depending on the drive requirements of the MOSFET and how fast you
        want it to switch, you may have to switch to a bipolar 555.
The degree to which the solenoids will interact depends on how
        tightly they're coupled, and rather than try to to predict how they
        might interact, it would be better to determine that empirically.
        That is, try it and measure the result(s)


Please post the data sheets - or links to their locations - for the solenoid, the MOSFET, and the flyback diode.

UPDATE:

Just for fun, here's your circuit redrawn so that it works, and simulated in LTspice:



Here are links to the files you'll need to run the sim. 
Download the files to the same folder, left-click on the .asc file to bring up the schematic and then left-click on the running man icon to start it.

Enjoy! :)

https://www.dropbox.com/s/avfi03sjc4h2e8n/AI555.asy?dl=0
https://www.dropbox.com/s/ip3rhu6qbllcpvj/Solenoid%20Driver.asc?dl=0