Would it harm a LiPo to charge it in several periods?
Charging the cell over shorter periods of time with a delay in between won't do any harm, in fact it may cause less heat and generally be better unless the period between each charge is so long that self-discharge comes into play, but that doesn't sound like it will be the case here.

However for testing the charger it also means you might not discover a thermal problem that only occurs after it has been running the full time. After the initial test if the end-of charge cut-off looks OK you might want to error on the side of caution and test in an environment with nothing flammable around (outside over concrete for example) so you can check temperatures towards the end of the charge cycle without having to be around to keep your eye on it during the earlier phase.