I hiked Imbros Gorge at 67 and found it GREAT It only took us about 4 hours and we stopped midway and had a picnic. We did it in late May, and the walls of the gorge were covered with thyme bushes... the scent was so strong, I felt like a leg of lamb in the oven!. During the entire walk we only encountered a dozen other hikers... it's because it isn't commercialized with bus tours like Samaria. And its not because it doesn't have amazing views. Near the bottom there is a super-narrow stretch... at one bend you go thru, if I'd had the arm-reach of an NBA star I could have touched both sides At the very end at the mouth of the gorge there was a lemonade stand. Then you walk on the road for about 1/3 mile... there's a sheer cliff to your left side, and you can see wild goats walking straight up it!! How??? Then you reach a taverna where there's a line of of "taxis" -- mainly pick-up trucks when we were there. They take u back up to the gorge entry for a negotiated fee (we paid €20 but that was 18 years ago)
Do take trekking sticks! They help so much with balance -- because the gorge path is all rocks ... ranging from soccer-ball size down to softball-size -- when you get to a stretch of just baseball-size that's real treat!. My friend had one but I had to grab a frail branch from a bush.. not good enough. if you don't have them, on Amazon there's a great brand "Earth-Trek" for $27 ... 4 segments held together with TOUGH central bungee cord... fold's up like a "W" into 12" into a plastic pocket, size of a hardcover book. Even has a "women's size" which is shorter. I took 2 in luggage in my 2019 trip and strode about with ease.
If you have 2 nights between 4 nights in Chania, and 2 nights in Iraklio area, you have many options. I use this map to help people plan - https://www.explorecrete.com/crete-maps/images/Crete-eot.png - click & it gets huuuge, navigate with side-slides. It show terrain & makes clear why u are limited in routes, due to mountains. From CHANIA to PHAISTOS -- I'd sugges taking "old Road" inland from Biggie N highway.. go thru tiny villages, still some goat herds on the road... Then from Rethymnon south on #97 (but dont look for roadside numbers there are none!) going thru SPILI -- stop for snack or lunch & fill water bottles at Lion Springs) If u want, u can take a Left @ Spili & drive down S. Side of the Amari Valley ... beautiful views... emerge near Ag Galini. U can spend night there... or forge on a bit farther, to Matala. Late in day, no tourists around. Don't stay at tacky hotels right onbeach shore.. Find lovely Dimitri Villa 750-1000 yds back.. landscaping, pool, mtn view, lovely family.
Next AM, have Matala swim, then go on to Phaistos & Gortyn. You'll be driving in Wine Harvest Time! Jump off #97 for Dafne, heart of vineyard country.. for a winey lunch... or dinner & find a local place to stay overnight. I"ve never fancied TWO nights in Iraklio, the Concrete City. Maybe 1 night near Knossos (arhanes?), see ruins early in AM, drive in to Iraklio, get Hotel on harbor, check in, drop car, go to Museum in late afternoon. I like Hotel Kronos, if you can get balcony overlooking the sea. Walk the causeway to the CASTLE, have dinner at ?Ippocampus?? early night to catch that 9:00/9:30 ferry to Santorini.