If I already donate 1 ETH during precontribution can I send/deposit more ETH as long as it comes from the same original wallet address that was reserved as TimeMint? I would like to start out with more DAY in my Mint.
Sure, it would work if you used the same address.
Is it also possible after the precontribution has ended?
No, the precontribution has ended, you can however get a TimeMint in the ICO itself, which will contains DAY tokens, and then transfer it back to your precontribution TimeMint or vice-versa