To be clear: "fibre top-up" is not MyRepublic-specific. Every fibre broadband provider can be affected by this.
For certain areas, OpenNet may discover they have not enough resources to support fibre broadband connections beyond a certain number. This happens when, for example, people switch from one fibre broadband provider to another or run multiple fibre lines.
To increase their capacity, OpenNet needs to top up their fibre resources, leading to a delay in getting your fibre broadband up and running. As more people go from one fibre broadband provider to another (as opposed to going from cable/ADSL to fibre), this issue is coming more common.
So yes, unfortunately your installation may be delayed to April.