In solidity we can use wei, gwei or ether as a suffix to a literal to be used to convert various ether based denominations. Lowest unit is wei and 1e12 represents 1 x 10^12.
Similar to currency, Solidity has time units where lowest unit is second and we can use seconds, minutes, hours, days and weeks as suffix to denote time.
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;
contract MyUnits {
// 1 wei == 1
// 1 gwei == 1e9
// 1 ether == 1e18
uint256 costOfNFT = 12.5 ether;
uint256 gasLimit = 3000 wei;
//1 == 1 seconds
//1 minutes == 60 seconds
//1 hours == 60 minutes
//1 days == 24 hours
//1 weeks == 7 days
uint256 durationOfMint = 7 days;
}