Sodium cyanoborohydride reductive amination troubleshooting

The compound is cyclic, is the timing of the reductive agent addition important here? I’ve seen written examples at ph 7-10, 6 and 5-7. My understanding is that at lower ph the reduction will occur without substitution.

It is impossible to comment this if you dont give details, are you making a primary or secondary amine etc.

Can you test it at different pHs small scale?

It seems you need pH 7-10?

https://en.wikipedia.org/wiki/Sodium_cyanoborohydride

I think if you have the imine in a equilibrium you will reduce it with NaBH3CN, you dont need to shift it completely.

Depends on the imine structure as well. 

Aromatic imines can be formed in water.  But all aliphatic hydrolyze readily.  So if you have a lot of water and aliphatic structures you will shift the equilibrium and have a lower concentration of imine and therefore slower reaction.