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State law decides most of what matters
The constitutional principle is national. Almost everything an owner actually needs to know, deadlines, procedure, whether business losses are compensable, whether fees shift, is state law and differs substantially.
Covered in depth
State sites in this network
Virginia
Procedure, compensation and the statutory framework.
North Carolina
Including the Map Act and the two separate condemnation procedures.
Florida
Including business damages, which Florida compensates by statute.
Texas
Procedure, the special commissioners hearing and landowner rights.
California
State and local condemnation practice.
Every other state
National doctrine and the questions that are the same everywhere.
If your state is not listed
Three reliable sources
Your state department of transportation. Highway projects account for a large share of all takings, and most state DOTs publish an owner guide explaining their acquisition process, the relocation programme and the timeline. It is written by the acquiring side and it is still accurate on procedure.
The state bar association. Many publish plain language guides to eminent domain for property owners, and most run a referral service that will find a lawyer who practises in the field.
A condemnation lawyer in your state. For the specific question of what deadline applies to the document you are holding, an hour of advice is the cheapest thing available and the most valuable.
Ask one question first: does this project have federal funding. If it does, the Uniform Relocation Act applies, which adds requirements the agency must meet regardless of state law.
Questions about state differences
Why does it matter so much which state I am in
Because the things that decide outcomes are state law: how long you have, whether possession precedes payment, whether your costs can be recovered and what counts as compensable loss.
Is the compensation standard the same everywhere
The constitutional floor is. States may be more generous and several are, particularly on business damages and on fee recovery.
Can I use a lawyer from another state
They will usually need local counsel. Procedure in condemnation is highly local and that is most of the value counsel adds.
Find the site that answers your question properly
This is a starting point. The detailed answers live on the sites built for each question, and on the site for your state.