Tummy time is great to 3 things. It strengthens the neck (and then later arms and shoulders), encourages hand strength and avoids flat spots on the back.
Sounds great! But some kids hate it. That's ok, there are other ways to get those benefits. Neck strength can be built by being held upright or being in a sling. This also reduces flat spots. Sitting on your lap is good for this too, but sitting in devices less so as they provide too much support for safety reasons.
Developing hand strength can be achieved through encouraging drumming/patting.
My eldest did almost no tummy time at all until 9 months, and then very little even then. Her tonsils were very large and it made breathing difficult for her so she just couldn't cope on her tummy. She didn't crawl, but was walking before a year and is a perfectly well coordinated 7 year old.
My twins were both ok with tummy time. As a result, they were good crawlers and didn't walk till much later. But aged there you coiodnt tell any difference between them and DD at that age.
DC4 we didn't do any tummy time between 1 month and months - she is quite refluxy and would just be sick everywhere! She's 5.5 months now and we've been doing some the last 2 weeks. She's barely behind those that have been doing it from day 1 and can raise up on her arms,roll from front to back and isnearly managing rolling back to front.
By all means do it if it works, it's good exercise for them. But if its not going as planned please don't worry, there are lots of other ways for your baby to strengthen their body.