*On the first sight this might look complicated, but it's not!*
Go to myetherwallet.com (WARNING! Always double check domain name and SSL details)
Push "Send Offline" button
Enter your ETH address so parameters can be pulled. You can do everything manually if you have good understanding of the gas concepts and Nonce concept. (WARNING: If you use the wrong nonce, the transaction won't go through! (read more about it here: https://www.reddit.com/r/ethereum/comments/6ihw6p/can_someone_please_explain_nonce_to_me/)
Myetherwallet will pull the nonce correctly for you as long as you don't make other transactions in the period between now and when you want to schedule your new transaction.
Looking at etherscan.io on your latest OUT transaction is another way to find your last Nonce. Your new Nonce is your last + 1. Example: If on your wallet the last OUT transaction has Nonce=120, you will have to use 121 for the next transaction.
Select gas limit and gas price. Most ICOs use smart contracts and you have to send 250000 gas limit to be on the safe side.
Gas price will be pulled from your last transaction, but always check what are the ICO conditions for gas price and how much are you willing to spend on gas. Miners are processing the higher gas transactions first. ( WARNING! myetherwallet.com offline transaction has the price in WEI and not on gwei like most wallets. Make sure you understand the difference and use https://etherconverter.online/ to double check.)
Access your wallet and sign the transaction after double checking all parameters are good.
Copy your signed transaction and submit it on the Chronobot website. Select execution time(Chronobot time is GMT) and submit your transaction.
At this point you don't have to worry about security as signed transactions are pretty much public info and nobody can steal your money or signature, all they can do is to execute the transaction faster than you intend.
Get a beer and enjoy your time, you no longer need to set alarm clocks and stress when to press the send button.