VAMPIR's dailies reset at 05:00 server time and its weeklies once a week, and missing a timed one, a world boss or the Arena, can't be made up later. Tick things off as you go. Enter your level to hide what isn't open yet; the ticks clear themselves at 05:00 on your device's clock each day and each Monday for the weeklies, and live in this browser only.
Give the timed content priority and hand the rest to Support Mode. Gehenna's first zone 1 entry each day is free, so take it even on a short day.
Support Mode works through daily quests first, then a Normal Dungeon, then field hunting, in that order. Set that routine once and most of the daily list runs itself while you do the timed content by hand.
Before you log off, start Offline Mode. It runs 8 hours free, or 24 with Olga's Grace, so park in a zone a little below your power where your potions last the whole stretch. Cap Support Mode at two or three deaths: you get five free EXP recoveries a day, and they are better kept for the deaths you take playing by hand.
Don't skip the timed ones
World bosses spawn at 12:00 and 20:00 server time, the same two slots the global client sets. Turn up to every one you can reach: the top 100 contributors get chests you can trade, and you must be in the zone when it dies to get anything. Donate to your clan three times a day for Clan Coins, which buy the Overlord portrait restorers.
On the weekly side, unused Epic Dungeon entries stop refilling at three, so run them every week. The Farming Diamond cap is 1,000 Farming Diamonds a week, shared by every character on the account and server, and it resets on Monday at 05:00 server time.