In case this is helpful - I had the same issue, but what I missed was - once I collected and activated bloodstones (I had 13 in total,) I had to:
1.) go to end of time
2.) have the conversation with Z/watch the cutscene
3.) GO TO THE NEWLY ACTIVATED PORTAL
4.) talk to Z and then go to the new portal
5.) then teleport out
6.) then teleport back
EVERY TIME.
Otherwise, no new portal opens. If you just clicked on all of the blood/starstones, and like me, you assume that opens all the portals. It doesn't. VERY STUPID DESIGN CHOICE.
