Is the block.timestamp value in Solidity seconds or milliseconds?

Question

I'm looking to use block.timestamp in one of my contracts and I want to know whether the block.timestamp is seconds like in Python or milliseconds like in Java or some other value?

Also, is it safe to use block.timestamp to check if 30 days is past since the last updated time or something like that?

Answer 1

From the Solidity documentation (here and here):

... timestamp of the current block in seconds since the epoch

For your other question:

Also, is it safe to use block.timestamp to check if 30 days is past since the last updated time or something like that?

Your question isn't completely clear, but assuming you're questioning the validity of a timestamp over a given period of time, then this previous answer should cover it: Is block.timestamp safe for longer time periods?

Answer 2

block.timestamp is a uint256 value in seconds since the epoch.

It's safe to compare like:

function f(uint start, uint daysAfter) {
    if (block.timestamp >= start + daysAfter * 1 days) { ... }
}

or

if (block.timestamp > start + 30 days) { ... }

Time units are helpful for some calculations with the caveat:

Take care if you perform calendar calculations using these units, because not every year equals 365 days and not even every day has 24 hours because of leap seconds. Due to the fact that leap seconds cannot be predicted, an exact calendar library has to be updated by an external oracle.

Answer 3

1-timestamp is the unix timestamp so to convert it to normal date use http://www.epochconverter.com/ it indicates when the block was created.

2-to answer if it is safer to use block.timestamp <30 days: yes because the miner could change the timestamp by 900 seconds.

Answer 4

block.timestamp may not be the correct time as it is set by the miner. Hence depends on the accuracy of the miners clock.

The current block.timestamp has to be more than the parent block.timestamp. This is set in the protocol. Some blocks even have 1s difference.

Blockchain has no clock as it would mean sync of all the nodes and that would be almost impossible to achieve.