1. Mom had to check the timer every 10 minutes.

2. Mom had to check the timer every 10th minute.

(Can we use both expressions?)

3. How about going at 6:00 at the art center.

4. How about coming at 6:00 at the art center.

5. How about arriving at 6:00 at the art center.

6. How about watching at 6:00 at the art center.

(Would you watch the ing forms? Are they grammatical from #3 to #6?)

2 answers

1, but not 2.

3, not 4. 5 - maybe. 6 is odd - watching what at 6:00?
1. is correct.

5. and 6. are correct.

3. and 4. You need to change the preposition to "to."