Since you have only 8 days, every single HOUR counts ... and going into Athens 2x wastes precious time! I gather you have not booked anything so why not consider what all of us "old hands" have learned --- it's most time-efficient if you save Athens for LAST. First place, it's more fun to recover from jet-weariness on an island ... 2nd, this means when you get to Athens y ou will already have "got the hang of Greece" and can more readily deal with a buzzing big city. So In your case I'd say, do this:
• DAY 1 - On Arrival, fly immediately to CHANIA (allow 1.5 or 2 hrs layover for getting your luggage, going to ATM, checking in to Aegean. You'll enjoy sunset on the harbor! Do not STAY on the harbor (or dine there); just have sunset drinks. Instead, stay 1 street OFF harbor -- Theotokopoulou Street ... it's a no-cars flagstoned lane, madly charming, leads right down to park by sea. 2 small hotels right on the seaward end of the Street, all good, both w balconies w. views: Hotel Palazzo, Hera Studios. Restaurants, for later. Use this great map http://www.explorecrete.com/crete-maps/images/Crete-eot.png (click & it gets huuuuge)
• DAY 2 - explore CHANIA 1/2 the day: good beach about 4km W of Chania Old Town -- local bus (or car rental) Another good dinner
• DAY 3 - Adventure! Dont do Samaria (takes whole day, which u don't have); instead, do Imbros: drive to top of gorge, walk down = 3+hrs (for young legs) get taxi to drive up rim-road back to your car. First, While on Lybian sea, have a swim! & if u want an adventure, take that Taxi to Komitades, hike down hillside to find a flower-covered stone 1200s-era church the size of a shed! ... I can give directions for that or other adventures & hikes
• DAY 4 - Drive E on BIG GREEN (the North coastal road)... Great swims on beach like Panormos; Go inland 5 mi and see Amazing Cave Melidoni -- historic, poignant (Turks martyred cretans there) ... Continue on BIG GREEN, bypass Heraklion, get to Knossos c 3pm? after Cruise throngs s have left, tour ruins w.o. crowds! Find yr way in to Heraklion (have a marked PAPER map), drop bags at Hotel (Kronos is good), zip over to Herak Museum for an hour. Walk out to Fortezza then have a Meze-delight dinner at Psara.
• DAY 5 - 9:45 ferry to SANTORINI arrive 11:45. Frankly my choice is to Stay in a caldera view hotel In FiroStephani (there are plenty of choices available in October) ... walkable to Fira shops, nightlife etc, but VERY serene (no tour busses). Fira-Oia hike NOT a must-do (it gets publicity mainly because its the only hike inSantorini). You can go to Oia for sunset if the ballyhoo has convinced you; I know better places, no crowds. If you DO go, reserve restaurant seat for sunset or you'll be a crowded standee.
• DAY 6 - early AM we always catch 8:30 bus to OIA - 90 serene minutes before cruise ship thousnds fill up the place... plenty of time to wander & take pix etc. When crowds arrive, u leave ... I would then advise getting an early afternoon flight to ATHENS for final 2 days.
• DAY 7 & 8 - I like SOUTH side of Acropolis... NO traffic (car-free promenade alongside ... 2 "sister" hotels, Hotel Herodion & Hotel PHillipos, both within a block or so of Acropolis museum o the Promenade -- hi floor balconies and/or roof terric of Herodion have great views; don't knw what their October rates are. This fine online Map - http://www.orangesmile.com/destinations/img/athens-map-big.jpg (ciick to Enlarge) shows how handy this is (Acrop Museum is #24 on Map)..
This sequence may not be what you had in mind, but you haven't done it before --- newcomer scenarios seldom allow for how much time transportation takes. Final tip: figure out LOGISTICS -- (planes, ferries) BEFORE you book hotels. There are always lodging options... there is not always Transport at the days times you want. You can buy ferry ticket day-of, but book any domestic flights ASAP. Restaurant, sightseeing tips -- that can come later.