Now
You cannot get the current time in LIGO but you can get the starting time of the current block :
const today: timestamp = Tezos.now;
Arithmetics
In LIGO, timestamps can be added to integers :
const today: timestamp = Tezos.now;
const one_day: int = 86_400;
const in_24_hrs: timestamp = today + one_day;
const some_date: timestamp = ("2000-01-01T10:10:10Z" as timestamp);
const one_day_later: timestamp = some_date + one_day;
const _24_hrs_ago: timestamp = today - one_day;
Comparison
You can compare timestamps using the same comparison operators applying to numbers.
const not_tommorow: bool = (Tezos.now == in_24_hrs);
Your mission
1- Compute the constant timestamp eta as our estimated time from arrival in 6 days from now.