you can take as long as you want to file a lawsuit in court, so long as its within the statute of limitaions.
Without the tenant knowing? Certainly. Being sued often comes as a surprise. Without the landlord knowing? ... that would be more difficult, but it's possible that someone in the landlord's office initiated the suit based on standard policy without the landlord being personally aware of the details.
can a landlord change the locks on a commercial building without notice
NO
Indentured servant.
Yes.
A brick
Yes.
If the landlord provided a key to the tenant, then the tenant must provide a key to the landlord. In fact, under most state laws the tenant may not change a lock without the landlord's permission and a duplicate key provided to the landlord.
Supreme Court
The landlord has self-remedies, up to a point. But landlords cannot issue a "legal judgement". The landlord can deduct damages and unpaid rent from your security deposit, and the landlord or tenant can seek legal resolution.
That depends on the municipality.
No, without a written lease, the landlord can only evict the same as a month to month lease agreement (30 days) but the protections to the tenant and landlord are not stated.