@Thorsten Behrens, I use TransactionSearch over 3 month window that moves forward by one week once per week. I've never experienced the "Jitter" you mention; eventually, all transactions show up. (The Ledger file I import to keeps track of which transactions have been seen before).
Ah ok, with that overlap, indeed you're safe. We'd hit the 100 transactions limit though sometimes for a single day, and stuff started to become fragile. Using the csv export since then, that also makes offline debugging easier. ;)