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1. How do I set the gwei higher than 99 in MEW?
You can't set gwei higher than 99 or you can only set max gwei allowed by mew UI/slider.
if you want to set custom gas/gwei use parity.
2. Is it possible to send a transaction before the starting time when the transaction hits after the starting time?
I'm not sure, but i think smart contract might reject your transaction if you send ETH before ICO starts. even if you send transaction early, you don't know it will confirm, before/after ICO start time!?