But: when the "Date" column in "History" tab is the confirmation time from Blockchain then where is the send time (=time when I send the transaction request to mempool)?
The Date column in "History" tab is the blocktime, i.e. the timestamp written in the blockheader of the block that includes the transaction. The blocktime can differ from the "real" confirmation time when the block was published to the network and acknowledged by all nodes which confirmed the block as valid.
The blocktime must be less than the
network adjusted time plus 2h AND it must be greater than the median time of the last 11 blocks. (Loosely quoted from
here.)
This translates roughly to a valid range of about -1h and upto +2h from the time the block was published. But in probably most of the time the blocktime is somewhere +/- one or two minutes max. from block publish time.
The timestamp in "Date" column: Which timezone is it?
It's in your local timezone of your OS running on your computer.