You're an architect. You're showing a couple an early version of the floor plans for their new house. It's easy to make changes to the plans now, but if they want to make changes later it will be difficult and expensive. So you say:
If you have any questions or concerns, now is the time to bring them up.
"Questions" and "concerns" are two words that often appear together:
If you have any further questions or concerns, please contact your HR representative.
Feel free to come to me with any questions or concerns you may have.
"Concerns" are things that you're worried about.
Use this phrase to talk about something that should be done now, instead of earlier or later.
You can use "now is the time to ___" to warn or inspire people:
Now is the time to buy. Home prices are at the lowest they've been in over 15 years.
Now is the time to invest in solar power initiatives.
Now is the time to make real the promises of democracy. Now is the time to rise from the dark and desolate valley of segregation to the sunlit path of racial justice. Now is the time to lift our nation from the quicksands of racial injustice to the solid rock of brotherhood. Now is the time to make justice a reality for all of God's children. (from a famous 1963 speech by Martin Luther King, Jr.)
When you "bring up" a topic, you start talking about it.
The phrase "bring up ___" is like many phrasal verbs. The word "up" immediately follows "bring" most of the time, like in this example:
I brought up the topic of Jessica, but he didn't seem like he wanted to talk about it.
But when you're using short words like "it", "her", "that", "something", etc. you put those words between "bring" and "up":
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