checking timestamp on bitcoin

[jscode017]

I'm curious that for every machine their time might be different, how can I sync my time with others, are there any way to check my time with others in bitcoin?

[BrewMaster]

accuracy is not the goal for timestamps that are used in different places on bitcoin network. so you shouldn't "sync your time" with others this way! try syncing your time to real time by using something like time.is website.

this talks about accuracy of it:
https://bitcoin.stackexchange.com/questions/20479/how-accurate-is-bitcoin-network-time

this talks about its usage:
https://bitcoin.stackexchange.com/questions/68653/the-role-of-timestamp

are there any way to check my time with others in bitcoin?

when you connect to another bitcoin core client, they send you an initial message called Version message which contains that node's date and time.

[ranochigo]

You don't have to have a synchronized time with others to use Bitcoin. Accuracy of the time is not a part of Bitcoin, it is usually wildly inaccurate. The network uses a network-adjusted time system. This means that the whole network can be up to 2 hours inaccurate (in unix time). If you are looking to adjust your clock, Bitcoin is not a good choice.

[jscode017]

thanks for the help!!
so i can make a assumption that time is hard to reach to consensus or being accurate in blockchain?

[Pmalek]

thanks for the help!!
so i can make a assumption that time is hard to reach to consensus or being accurate in blockchain?

Yes, as ranochigo said it can be very inaccurate and shouldn't be relied upon.
"Network time is never adjusted more than 70 minutes from local system time".

You can read a bit about it here:
https://en.bitcoin.it/wiki/Block_timestamp

[jscode017]

thanks 

[jscode017]

May I ask another one?
Then how does the time expire works? Given that each node have different time?

[ranochigo]

May I ask another one?
Then how does the time expire works? Given that each node have different time?

There's two ways, UNIX time stamp or Block height.

With the UNIX code, the nodes will check the transactions in the block against the timestamp of the block. If the timestamp of the transaction is lower than the timestamp of the block, the whole block becomes invalid. Blocks can be up to 2 hours inaccurate.

For the block height, the transactions that is in the block must at least meet the block height of the block that it is in. If not, it is invalid.

[jscode017]

Thanks a lot!!!