Well, you can make your 'emulated IB Algo' as complicated as you like. To start with a timer (like I described above) seems like the simplest and most logical choice.
To make you algo 'smarter' you can also look how the market ('last') price is moving. If the current price is moving towards your limit price, you can simply sit and wait and 'let the market come to you'. If market price is moving away from your current limit price, you have to decide how bad you want the order filled. If you want very much to have the order filled, you must 'chase the market' and move your limit price faster towards the market price ...
That's why the IB Algo has this 'aggressiveness' parameter.
You could for example create a parameter in your algo, that specifies the 'change rate' of your limit price. That would be 'how much cents per minute' you want your limit to change. A high change rate would compare with a high aggressiveness in the IB Algo ....
What I describe above is basically how I fill my orders manually. I start with a limit price that is very much in my favour (right at the bid or ask price), and start changing the limit price until filled. With a liquid security that is usually around the mid price. And with options it is usually also very close to the model price that my orders are filled.
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