I guess if you're looking for something simple you can look at the current block height and set the locktime field of the transaction to be N+current_height, N being the number of blocks you want the transaction to stay unconfirmed since it won't be included in any block before the N+current_height'th one.

A block takes on average 10 minutes to mine so a better value that would correspond to X hours is X*10*6 blocks: locktime=X*10*6+current_height.

That way there is blockchain proof that the transaction is pending and if whatever deal you have doesn't complete by then you can double-spend it back to yourself with a larger fee.