New wood siding--stain now or later?

My contractor has taken far longer to side my cottage with white cedar shiplap than I expected--started 6 weeks ago. He should be done by the end of this week but in northern Michigan the temps barely hit 70 right now with overnight lows in the upper 40's. I have Sikkens SRD penetrating stain/finish (transparent natural color) on hand but I'm concerned it might be too late to apply.

Should I wait till warmer weather next May or so...and will this mean extra steps if the siding turns grey by then?
Should I consult with the mfr on this?

The instructions on the can should say if there's a min/max temperature for installation. If you're within the range, it should be okay. A stain may not have a min. If you like the color of the wood now, it's best to protect it now.

The tech support of the manufacturer is a good place to start after you've fully read the instructions on the can.