Please do not get your hopes up too high about the property!
Because...
We are looking in a small area near Frankfurt.
and...
We want to offer about 20-25% above the standard land value.
are mutually exclusive.
The standard land values are updated far too slowly. Methodologically. The period used to form local average prices is too long to realistically reflect the extreme price increase of recent years in the standard land value. Too many "old" sales are still included in the calculation.
Just write specifically in the email that you are orienting yourself on the standard land value + X. Before he decides, he should please get back to you so that you can possibly increase your offer.
Deadlines etc. are pointless, he will just laugh if his property is really good (location, condition and proximity to Frankfurt).
PS. we also participated in such a bidding process and the reaction was only: we will not be considered because the bid was way too low. (The bid was also significantly above the standard land value). There was not even the question whether we wanted to increase...