Showing months elapsed in Gantt chart timeline?

Question

I'd like to render a monthly Gantt chart with the number of months elapsed rather than the name of the year and month. (This is used for proposals: The project could be funded one quarter, or the next, so you have to give elapsed time rather than absolute date.) For example:

@startgantt
projectscale monthly
Project starts 2024-3-1

[Task1] starts 1 March 2024 and lasts 90 days
then [Task2] lasts 90 days
@endgantt

Generates an image with the timeline on the top like:

2024

March        |        April        |       May       |      June       |       July      |       August

I'd like it to look like:

1          |           2          |          3          |         4         |         5         |           6

How can this be changed? Is there a localization that results in just months elapsed?