When my eldest g.daughter was born, her Mum was in the middle of taking her degree and working part-time (NHS). Babies, dad was still living in their house, but was unemployed, clinically depressed and drinking a lot. No way would my daughter let him (and he agreed) have sole charge of a small baby.
So, it was down to me to provide that care for a couple of days each week, when she had to return to work. From six weeks old, bottles of breast milk in fridge. From three months this also meant that baby had to go to child minder for a further two days each week (I also had a part-time job).
It was hard (not for baby who thrived) but for Mum.
Research has shown that Mums usually need their babies, more than babies need their Mums. Babies can happily make good relationships with several adults.
Sadly, the Dad died a few years back (alcohol related cancer), but my daughter went on to gain a first class degree and has a very excellent career in the NHS. Her daughter is in final year of A levels, planning to go to Uni to take a Social Worker degree/qualification. She is a happy, healthy, extremely well adjusted teenager. It has meant that I have a wonderful relationship with her due to the fact that i was her second carer right through her childhood.
I think it has always been important to give new Mums and Dads, sometime away from Baby. More than an hour or two they are likely to find difficult, but to have freedom to get a long shower, a pampering time, an 'us' time can be beneficial to them and to baby.
So Loodl my suggestion to you, is to thoroughly enjoy your new 'grandparent' status, and enjoy your g.child. Give what support is required, when it is required to your daughter and look forward to many, many years of child sitting and have fun.