I have a saying,
Watch your baby, not the clock.
It is important to watch your little one and respond to their cues.
Babies don't always love being alone on their tummy. If your bub isn't a fan I would encourage you to help them practice tummy time in little bits often, like rolling over after a nappy change and having an eye to eye chat.
And if your respond to their little noises and signals of happiness they will know you are there to help and instead of becoming more and more frustrated, they will more likely build their tolerance of tummy time.
Sometimes it can feel like you do micro tummy time sessions at 1 month, 2 months and 3 months before things just click. This is ok, your little one is learning about their body and this big world and the most important things is your relationship, building that security and attachment.