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# Algorand Specifications

The timestamp tt is a 64-bit signed integer.

The timestamp is purely informational and states when a block was first proposed,
expressed in the number of seconds since the Unix epoch (00:00:00 UTC on Thursday,
1 January 1970).

The timestamp tr+1 of a block in round r is valid if:

- tr=0 or
- tr+1>tr and tr+1<tr+Δtmax.

> Important
>
> **EXAMPLE:**
>
> Suppose the block production stalls on round r for a prolonged time. When
> correct operations resume, a certain number n of blocks has to be committed
> until the timestamp catches up to external time references. If t∗
> is the current external time reference, then:
>
> n=⌈t∗−trΔtmax⌉