So you've already cleared other endings and just restart from day 60 from there? I have a feeling you may have missed 1 or 2 things that need to be done before day 60 but you haven't done it in your previous endings so now you can't do it by just restart from day 60. It'd be easier if you restart from day 1 (you still keep your level and items anyway, only need to redo quests).
About that slum quest, yes the instruction about 5 days worth of food is a bit unclear. It's actually like this: "Give them 5 days worth of food, wait for them to eat all of it. Then after 5 days, return and give them 5 more days of food to trigger an event. Then after 5 more days, return and give them more foods to trigger the last event." After this you're done. You actually need 15 days, not 5.
Below are the detailed instruction for TRUE END. Please check to make sure you haven't missed anything:
Congratulation, you've achieved TRUE END. Also, please try clearing TRUE END while keeping Alcy as a VIRGIN. You'll get a very useful item for the DLC.