Sprintime, no, you have absolutely not lost any window :)
Sometimes, formula is advised on maternity units to deal with a short-term crisis - but it only needs to be temporary.
To get back to full bf, keep your baby close and snuggled in, skin to skin, so you can respond immediately to her feeding cues any time when she is not deeply asleep. Don't expect her to settle anywhere but next to you - if she's been a bit poorly and lethargic, plus a difficult time with the birth, she needs to make up for lost time, and she needs to be close to you. She will object when put down away from you - yay! This is good!
Less than a week ago she was inside you feeding much of the time. A three hour feedathon can be normal in these early days - she will be dosing and snoozing during that time, but only really happy on or near the breast. Normal.
Is there a midwife seeing you (I'm assuming you're at home now) who can support you in not giving formula and working your way back to full bf?
You can also call any of the bf helplines.
Hope today is better for you.