What would you like to be added

Add a deadline(e.g. 1s) for mint block. If deadline is reached, mint block should complete immediately

Why is this needed

make sure low hardware delegates can propose a block in time when a mass of actions

How important you think this is for IoTeX

• [] must have
• [] should have
• nice to have

Additional information

Let us know any background or context that would help us better understand the request (for example the particular use-case that prompted this request)