Indefinite length trial period

We would like to offer our clients free hosting during the development period of their website (as we need a hosting account during development). Given each website takes a different amount of time to complete, we have no idea how long this period may be.

I assume the best way to do this is have a free plan and a pay plan. Start them on the free plan, them move them to the pay plan once development is complete.

But at the time we switch, we would want the billing period to begin so they get charged the full amount for a full billing period.

Would the following sequence work?

1. Start on free plan. Once development is complete...
2. Make sure the free plan is set to the billing period desired (in our case, that's monthly, annual or 2 years).
3. Set the free plan's Period Starting Date to whatever the date is of the switch.
4. Switch plans to the pay plan.

Say the annual fee was $100. If we follow that sequence would the client be charged $100 at the time of the switch?

This is a good question and outside of my specialty I am going to refer it to the billing dept and see if they know how this may be best achieved.

You could maybe start them on the paid plan but give them a manual credit each month until you're ready to charge? You can use your own email for their account until then so that they're not getting billing emails.

That sounds like a pain in ass. Not only do you have to make all those credits every month for every project, if they go live in the middle of a billing period, you'd have to calculate the partial month amount to add back as an additional service and that would have to based on the billing cycle they choose.