The question underneath most first messages is "will she answer, and when". Here is what the data on this site says, in general terms, because the specific numbers belong to the women and not to me.
Most replies come within the first few hours, and the fastest come in the Thai afternoon, between the time she wakes and the time her shift starts. Messages sent during her shift are read late at night or the next day. Messages sent at her three in the morning are read at her noon.
If you are in Europe, your lunchtime is her late afternoon. If you are in the United States, your late evening is her afternoon. Australia is nearly on her clock. Send then and you are writing into the part of her day when she is on her phone and not at work.
Usually nothing. A slow reply means she was working, sleeping, at the market, or with her child. It does not mean the message was bad. Wait a day before you write again, and when you do, do not ask why she took so long.
She reads Thai on the phone she already uses and answers in Thai. The translation happens in the middle, so a reply costs her one sentence rather than a session with a translator. Every page on this site shows how quickly she usually answers, worked out from her own replies, so you know before you write.
The short version: write in her afternoon, keep it short, and give her a day. Most of the time she answers.